Sample records for redox multi-wall carbon

We report chemical vapor deposition (CVD) growth of a multi-walledcarbon nanotube (MWCNT) inside another MWCNTs from a cementite (Fe3C) catalyst nanoparticles. The CNTs have bi or tri-layered core(s)-sheath structure with various crystallinity. The sheath grows first at a lower temperature, and then the catalyst nanoparticle works again to grow the core(s) at a higher temperature in the tip or root growth mode. Transmission electron microscopy (TEM) observation provides a clear piece of evidence of reverse-inward growth. PMID:26353735

In this work, the cutting of carbon nanotubes is investigated using silver nanoparticles deposited on arc discharge multi-walledcarbon nanotubes. The composite is subsequently heated in air to fabricate shortened multi-walled nanotubes. Complementary transmission electron microscopy and spectroscopy techniques shed light on the cutting mechanism. The nanotube cutting is catalysed by the fundamental mechanism based on the coordination of the silver atoms to the π-bonds of carbon nanotubes. As a result of the metal coordination, the strength of the carbon-carbon bond is reduced, promoting the oxidation of carbon at lower temperature when heated in air, or lowering the activation energy required for the removal of carbon atoms by electron beam irradiation, assuring in both cases the cutting of the nanotubes. PMID:26987452

In this work, the cutting of carbon nanotubes is investigated using silver nanoparticles deposited on arc discharge multi-walledcarbon nanotubes. The composite is subsequently heated in air to fabricate shortened multi-walled nanotubes. Complementary transmission electron microscopy and spectroscopy techniques shed light on the cutting mechanism. The nanotube cutting is catalysed by the fundamental mechanism based on the coordination of the silver atoms to the π-bonds of carbon nanotubes. As a result of the metal coordination, the strength of the carbon-carbon bond is reduced, promoting the oxidation of carbon at lower temperature when heated in air, or lowering the activation energy required for the removal of carbon atoms by electron beam irradiation, assuring in both cases the cutting of the nanotubes.

Understanding of the effect of the multi-walledcarbon nanotube (MWCNT) dispersion process on physical properties of MWCNT film is crucial in process optimization of MWCNT film-based products. In the present work, the electrical conduction property of MWCNT films according to various conditions in MWCNT dispersion is investigated. Spectroscopic analysis of dispersed MWCNTs show that the electrical resistance of the MWCNT conductive film is affected by an increase in the electrical contacts between adjacent CNTs due to CNT debundling and physical damage caused by ultrasonic processing. Based on the two conflicting parameters, dispersion guidelines for highly conductive MWCNT film are presented. PMID:22849134

High strain rate experiments performed on multi-walledcarbon nanotubes, polycarbonate composites (MWCNT-PC) have exhibited enhanced impact resistance under a dynamic strain rate of nearly 2500/s with composition of only 0.5 to 2.0% multi-walledcarbon nanotubes (MWCNTs) in pure polycarbonate (PC). Similarly, hardness and elastic modulus under static loads resulted in a significant increase, depending upon the composition of MWCNTs in PC. The present work aims to analyze these results by correlating the data to fit expressions in generalizing the behavior of MWCNTs composition for MWCNT-PC composites under both static and impact loads. As a result, we found that an optimum composition of 2.1 weight % of MWCNTs exhibits maximum stress resistance within elastic range under strain rates of nearly 2500/s for MWCNT-PC composites. The composition of MWCNTs plays a crucial role in maximizing modification of static and dynamic impact-based mechanical properties of polycarbonates. Further, a simple model based on Lennard-Jones 6-12 atom-atom based potential is formulated and used to compute preliminary estimates of static properties of pure as well as composite PC with the aim to modify this in subsequent approaches.

Current diagnostic techniques do not reliably detect cancer at early stages, and traditional chemotherapy lacks specificity and causes systemic toxicity. To address these issues, multifunctional nanomaterials are becoming more widely studied as a means of cancer detection, therapy, and monitoring. Here, iron oxide (Fe3O4) nanoparticles were conjugated onto the surface of multi-walledcarbon nanotubes (MWNTs), which were then modified with polyethylenimine (PEI) and polyethylene glycol (PEG) to improve their solubility and biocompatibility. Finally, human telomerase reverse transcriptase (hTERT) siRNA was loaded on the MWNT surface by electrostatic interaction to obtain a multifunctional delivery system (MWNT-Fe3O4-PEI-PEG/siRNA). This delivery system efficiently delivered siRNA, allowed targeting of certain sites by magnetic fields, facilitated photothermal heating by near infrared irradiation, and enabled magnetic resonance imaging, thereby indicating great potential for cancer theranostic applications. PMID:26485934

We report on the synthesis and electrochemical properties of multi-walledcarbon nanotubes (MWCNTs) for supercapacitor devices. Freestanding vertically-aligned MWCNTs and MWCNT powder were grown concomitantly in a one-step chemical vapour deposition process. Samples were characterized by scanning and transmission electron microscopies and Fourier transform infrared and Raman spectroscopies. At similar film thicknesses and surface areas, the freestanding MWCNT electrodes showed higher electrochemical capacitance and gravimetric specific energy and power than the randomly-packed nanoparticle-based electrodes. This suggests that more ordered electrode film architectures facilitate faster electron and ion transport during the charge-discharge processes. Energy storage and supply or supercapacitor devices made from these materials could bridge the gap between rechargeable batteries and conventional high-power electrostatic capacitors.

A novel and effective method was devised for synthesizing a vertically aligned carbon nanotube (CNT) forest on a substrate using waste plastic obtained from commercially available water bottles. The advantages of the proposed method are the speed of processing and the use of waste as a raw material. A mechanism for the CNT growth was also proposed. The growth rate of the CNT forest was ~2.5 μm min-1. Transmission electron microscopy images indicated that the outer diameters of the CNTs were 20-30 nm on average. The intensity ratio of the G and D Raman bands was 1.27 for the vertically aligned CNT forest. The Raman spectrum showed that the wall graphitization of the CNTs, synthesized via the proposed method was slightly higher than that of commercially available multi-walledcarbon nanotubes (MWCNTs). We expect that the proposed method can be easily adapted to the disposal of other refuse materials and applied to MWCNT production industries.

Apparatus (210) for producing a multi-wallcarbon nanotube (213) may comprise a process chamber (216), a furnace (217) operatively associated with the process chamber (216), and at least one filament (218) positioned within the process chamber (216). At least one power supply (220) operatively associated with the at least one filament (218) heats the at least one filament (218) to a process temperature. A gaseous carbon precursor material (214) operatively associated with the process chamber (216) provides carbon for forming the multi-wallcarbon nanotube (213). A metal catalyst material (224) operatively associated with the process (216) catalyzes the formation of the multi-wallcarbon nanotube (213).

The aim of this study is utilizing the artificial photosynthesis, which is an attractive and challenging theme in the photoelectrocatalytic water splitting, to charge the vanadium redox flow battery (VRFB). In this work multiwalledcarbon nanotube/cadmium sulphide hybrid is employed as a photoanode material to oxidize VO2+ to VO2+ for charging the positive vanadium redox flow battery's half-cell. Characterization studies are also described using the scanning electron microscopic-energy-dispersive X-ray spectroscopy (SEM-EDS), inductively coupled plasma atomic emission spectroscopy (ICP-AES) and UV-Visible methods. The phtoelectrochemical performance is characterized by cyclic voltammetry and chronoamperometry. Applied bias photon-to-current efficiency (ABPE) is achieved for both two and three-electrode configurations. The glassy carbon/multiwalledcarbon nanotube/cadmium sulphide yields high maximum ABPE of 2.6% and 2.12% in three and two-electrode setups, respectively. These results provide a useful guideline in designing photoelectrochemical cells for charging the vanadium redox flow batteries by sunlight as a low cost, free and abundant energy source, which does not rely on an external power input.

CVD grown MWCNTs, of typical diameter 5 to 50 nm and with approximately 15-20 concentric graphene layers in the multi-walls, have been surface functionalised using the Fenton hydroxylation reaction. HRTEM reveals little physical difference between the treated and untreated materials; images from both exhibit similar multi-wall structure and contain evidence for some low-level disruption of the very outermost layers. Raman spectra from the two types of nanotubes are almost identical displaying the disorder (D) peaks at approximately 1350 cm{sup -1} and graphite (G) peaks at approximately 1580 cm{sup -1}, characteristic of graphene-based carbon materials, in approximately equal intensity ratios. Equilibrium adsorption data for nitrogen at 77 K leads to BET surface areas of 60.4 m{sup 2} g{sup -1} for the untreated and 71.8 m{sup 2} g{sup -1} for the hydroxylated samples; the increase in area being due to separation of the tube-bundles during functionalization. This is accompanied by a decrease in measured porosity, mostly at high relative pressures of nitrogen, i.e. where larger (meso 2-5 nm and macro >5 nm) pores are being filled, which is consistent with an attendant loss of inter-tube capillarity. X-ray photoelectron spectroscopy (XPS) shows that hydroxylation increases the nanotube surface oxygen level from 4.3 at.% to 22.3 at.%; chemical shift data indicate that approximately 75% of that oxygen is present as hydroxyl (-OH) groups. Water vapour adsorption by the hydroxylated surfaces leads to Type II isotherms which are characteristic of relatively high numbers of hydrogen bonding interactions compared to the untreated materials which exhibit Type III curves. This difference in polar surface energy is confirmed by calorimetric enthalpies of immersion in water which are -54 mJ m{sup -2} for the untreated and -192 mJ m{sup -2} for the hydroxylated materials. The treated materials therefore have significantly increased water wettability/dispersivity and a greater

Engineered multi-walledcarbon nanotubes (MWCNTs) are the subject of intense research and are expected to gain widespread usage in a broad variety of commercial products. However concerns have been raised regarding their potential environmental and health risks. The mobility of MWCNTs in porous media is examined in this study through one dimensional flow-through column experiments under conditions representative of subsurface and drinking water treatment systems. The goal of this work was to determine dominant MWCNT removal mechanisms and factors that control MWCNT transport. Results demonstrate that pore water velocity strongly influenced MWCNT transport, a result that stands in contrast to traditional colloid filtration theory, which suggests a relatively minor effect of flow velocity in comparison to Brownian diffusion. Experiments conducted at different ionic strengths indicate that both particle deposition and straining are important MWCNT removal mechanisms from the aqueous phase. Given these findings, traditional colloid filtration theory may not be appropriate for the prediction of MWCNT mobility in porous media. This may be due to the large aspect ratio of the MWCNTs and the importance of straining in MWCNT removal.

A novel application that utilizes conductive patches composed of purified multi-walledcarbon nanotubes (MWCNTs) embedded in a sodium cholate composite thin film to create microstrip antennas operating in the microwave frequency regime is proposed. The MWCNTs are suspended in an adhesive solvent to form a conductive ink that is printed on flexible polymer substrates. The DC conductivity of the printed patches was measured by the four probe technique and the complex relative permittivity was measured by an Agilent E5071B probe. The commercial software package, CST Microwave Studio (MWS), was used to simulate the proposed antennas based on the measured constitutive parameters. An excellent agreement of less than 0.2% difference in resonant frequency is shown. Simulated and measured results were also compared against identical microstrip antennas that utilize copper conducting patches. The proposed MWCNT-based antennas demonstrate a 5.6% to 2.2% increase in bandwidth, with respect to their corresponding copper-based prototypes, without significant degradation in gain and/or far-field radiation patterns.

The pristine multi-walledcarbon nanotubes (MWCNTs) were oxidized by the ultrasonication process. The oxidized MWCNTs were characterized by the X-ray diffraction (XRD), ultraviolet-visible (UV-Vis) and Fourier transform -Raman (FT-Raman) spectroscopic techniques. The XRD analysis confirms that the oxidized MWCNTs exist in a hexagonal structure and the sharp XRD peak corresponds to the (002) Bragg's reflection plane, which indicates that the MWCNTs have higher crystalline nature. The UV-Vis analysis confirms that the MWCNTs functionalized with the carboxylic acid. The red shift was observed corresponds to the D band in the Raman spectrum, which reveals that the reduced disordered graphitic structure of oxidized MWCNTs. The strong Raman peak was observed at 2563 cm-1 corresponds to the overtone of the D band, which is the characteristic vibrational mode of oxidized MWCNTs. The carboxylic acid functionalization of MWCNTs enhances the dispersibility, which paves the way for potential applications in the field of biosensors and targeted drug delivery.

The physicochemical properties of nanomaterials play crucial roles in determining their biological effects. Agglomeration of nanomaterials in various systems is a common phenomenon, however, how agglomeration affects the biological consequence of nanomaterials has not been well investigated because of its complexity. Herein, we prepared variable sized agglomerates of oxidized multi-walledcarbon nanotubes (O-MWCNTs) by using Ca(2+) and studied their cellular uptake and cytotoxicity in HeLa cells. We found the altered property of O-MWCNTs agglomerates could be controlled and adjusted by the amount of Ca(2+). Agglomeration remarkably facilitated the cellular uptake of O-MWCNTs at the initial contact stage, due to the easy contact of agglomerates with cells. But agglomeration did not induce evident cytotoxicity when the concentration of O-MWCNTs was less than 150μg/mL. That was assayed by cell proliferation, membrane integrity, apoptosis and ROS generation. This study suggests us that the biological behaviors of nanomaterials could be altered by their states of agglomeration. PMID:26930035

This study intends to develop protocols for sampling and characterizing multi-walledcarbon nanotube (MWCNT) aerosols in workplaces or during inhalation studies. Manufactured dry powder containing MWCNT’s, combined with soot and metal catalysts, form complex morphologies and diverse shapes. The aerosols, examined in this study, were produced using an acoustical generator. Representative samples were collected from an exposure chamber using filters and a cascade impactor for microscopic and gravimetric analyses. Results from filters showed that a density of 0.008–0.10 particles per µm2 filter surface provided adequate samples for particle counting and sizing. Microscopic counting indicated that MWCNT’s, resuspended at a concentration of 10 mg/m3, contained 2.7 × 104 particles/cm3. Each particle structure contained an average of 18 nanotubes, resulting in a total of 4.9 × 105 nanotubes/cm3. In addition, fibrous particles within the aerosol had a count median length of 3.04 µm and a width of 100.3 nm, while the isometric particles had a count median diameter of 0.90 µm. A combination of impactor and microscopic measurements established that the mass median aerodynamic diameter of the mixture was 1.5 µm. It was also determined that the mean effective density of well-defined isometric particles was between 0.71 and 0.88 g/cm3, and the mean shape factor of individual nanotubes was between 1.94 and 2.71. The information obtained from this study can be used for designing animal inhalation exposure studies and adopted as guidance for sampling and characterizing MWCNT aerosols in workplaces. The measurement scheme should be relevant for any carbon nanotube aerosol. PMID:23033994

Boron-doped multi-walledcarbon nanotubes were synthesized upon decomposition of ethyl alcohol and boric acid via chemical vapor deposition. The boron-doped nanotubes were treated with hydrochloric acid and were characterized by means of scanning electron and transmission electron microscopy in conjunction with energy-dispersive X-ray spectrometry and X-ray photoelectron spectroscopy. The electrochemistry of ferrocyanide/ferricyanide on boron-doped nanotubes was studied in temperature range of 283.15-303.15 K. The findings exhibit an improvement of films' current response and kinetics of electron transfer with the rise in temperature. The kinetics for electron transfer enhances and the redox process occurs slightly more spontaneously upon acid treatment.

The covalent functionalization of multi-walledcarbon nanotubes (MWCNTs) with a proline-based derivative is reported. Initially, MWCNTs were oxidized in order to introduce a large number of carboxylic units on their tips followed by N-tert-butoxycarbonyl-2,2'(ethylenedioxy)bis-(ethylamine) conjugation through an amide bond. Then, a proline derivative bearing a carboxylic terminal moiety at the 4-position was coupled furnishing proline-modified MWCNTs. This new hybrid material was fully characterized by spectroscopic and microscopy means and its catalytic activity in the asymmetric aldol reaction between acetone and 4-nitrobenzaldehyde was evaluated for the first time, showing to proceed almost quantitatively in aqueous media. Furthermore, several amino-modified MWCNTs were prepared and examined in the particular aldol reaction. These new hybrid materials exhibited an enhanced catalytic activity in water, contrasting with the pristine MWCNTs as well as the parent organic molecule, which failed to catalyze the reaction efficiently. Furthermore, the modified MWCNTs proved to catalyze the aldol reaction even after three repetitive cycles. Overall, a green approach for the aldol reaction is presented, where water can be employed as the solvent and modified MWCNTs can be used as catalysts, which can be successfully recovered and reused, while their catalytic activity is retained.The covalent functionalization of multi-walledcarbon nanotubes (MWCNTs) with a proline-based derivative is reported. Initially, MWCNTs were oxidized in order to introduce a large number of carboxylic units on their tips followed by N-tert-butoxycarbonyl-2,2'(ethylenedioxy)bis-(ethylamine) conjugation through an amide bond. Then, a proline derivative bearing a carboxylic terminal moiety at the 4-position was coupled furnishing proline-modified MWCNTs. This new hybrid material was fully characterized by spectroscopic and microscopy means and its catalytic activity in the asymmetric aldol reaction

The hepatotoxicity of two types of multi-walledcarbon nanotubes (MWCNTs), acid-oxidized MWCNTs (O-MWCNTs) and Tween-80-dispersed MWCNTs (T-MWCNTs), were investigated with Kunming mice exposed to 10 and 60 mg kg-1 by intravenous injection for 15 and 60 d. Compared with the PBS group, the body-weight gain of the mice decreased and the level of total bilirubin and aspartate aminotransferase increased in the MWCNT-exposed group with a significant dose-effect relationship, while tumor necrosis factor alpha level did not show significant statistical change within 60 d. Spotty necrosis, inflammatory cell infiltration in portal region, hepatocyte mitochondria swelling and lysis were observed with a significant dose-effect relationship in the MWCNT groups. Liver damage of the T-MWCNT group was more severe than that of the O-MWCNT group according to the Roenigk classification system. Furthermore, T-MWCNTs induce slight liver oxidative damage in mice at 15 d, which was recovered at 60 d. Part of the gene expressions of mouse liver in the MWCNT groups changed compared to the PBS group, including GPCRs (G protein-coupled receptors), cholesterol biosynthesis, metabolism by cytochrome P450, natural-killer-cell-mediated cytotoxicity, TNF- α, NF-κB signaling pathway, etc. In the P450 pathway, the gene expressions of Gsta2 (down-regulated), Cyp2B19 (up-regulated) and Cyp2C50 (down-regulated) had significant changes in the MWCNT groups. These results show that a high dose of T-MWCNTs can induce hepatic toxicity in mice while O-MWCNTs seem to have less toxicity.

The increasing production and applications of multi-walledcarbon nanotubes (MWCNTs) have elicited concerns regarding their release and potential adverse effects in the environment. To form stable aqueous MWCNTs suspensions, surfactants are often employed to facilitate dispersion...

Direct oxidation of tryptophan on multi-wallcarbon nanotubes modified glassy carbon electrode was examined. Surface poisoning, which was suppression of oxidative current caused from adsorption of oxidized compounds of amino acids through multiple redox scan, was observed on carbon material electrodes (multi-wallcarbon nano tube(CNT), carbon powder(CP), Ketjen Black (KB) and glassy carbon(GC). It was found that CNT showed a highly inhibitory effect on the surface poisoning and high current value in the direct oxidation of tryptophan because of a π-π interaction between CNT and indole ring of tryptophan results from orbital mixing. This CNT modified GC electrode was applied to an anode in a fuel cell used with amino acids as fuel. As a result, the maximum of the power density showed 0.36 mW cm-2 at 2.5 mA cm-2 of the current density and 140 mV of the cell voltage.

Multi-walledcarbon nanotubes with rectangular or square cross-section are formed. The nanotubes are about 50-200 nm in width, and their walls are around 5-30 nm thick. It is very likely that the rectangular cross-section is shaped simultaneously when nanotubes are formed from catalyst Fe nanoparticles during chemical vapor deposition process, and the shape is stabilized by the bonding between adjoining graphene layers in the multi-walled structure.

This paper describes a disposable electrochemical biosensor for glucose monitoring. The sensor was based on multi-wallcarbon nanotubes (MWCNTs) immobilized with glucose oxidase and upon screen printed carbon electrode. The effect of MWCNTs on the response of amperometric glucose oxidase electrode for glucose was examined. Results obtained, of interest for basic and applied biochemistry, represent a first step in construction of a MWCNT-enzyme electrode biosensor with potentialities for a successful application in the biosensor area. PMID:16076441

Carbon nanotubes with superior mechanical, electrical and thermal properties have received intensive attention in recent years. In this study, multi-walledcarbon nanotubes (MWCNT) were infused into a liquid epoxy, and the solution was sonicated for three hours to separate the aggregation of the MWCNTs and achieve good dispersion. The trapped air was removed from the mixture using a high vacuum. To investigate the effect of matrix stiffness on the mechanical properties of the MWCNT nanocomposites, the mixture ratio between the epoxy and hardener was varied. Two different contents (1% wt. and 2% wt.) of the multi-walledcarbon nanotubes were added into the epoxy matrix. Tensile tests were conducted to determine the Young's modulus, yielding stress and tensile strength of the nanocomposites. The natural frequency and damping ratio of the nanocomposites were evaluated using free vibration tests. Experimental results show that the Young's modulus and natural frequency of MWCNT/epoxy nanocomposites increase with increase of the addition of multi-walledcarbon nanotubes. While the damping ratio of the nanocomposites decreases with increase of the multi-walledcarbon nanotubes. The reinforcement role of the multi-walledcarbon nanotubes is less significant in a hard matrix when compares with a soft matrix. PMID:23421186

Applications of nanomaterials, including carbon nanotubes (CNTs), are increasing; however, their impact on the environment is still not well understood. A semi-arid soil was treated with multi-walledcarbon nanotubes (MWCNTs) at four different concentrations (10-10000 mgMWCNTs kg-1soil), and incubat...

Local inflammatory response in the lungs and fibrogenic potential of multi-walledcarbon nanotubes were studied in an acute aspiration experiment in mice. The doses were chosen based on the concentration of nanotubes in the air at a workplace of the company-producer. ELISA, flow cytometry, enhanced darkfield microscopy, and histological examination showed that multi-walledcarbon nanotubes induced local inflammation, oxidative stress, and connective tissue growth (fibrosis). Serum levels of TGF-β1 and osteopontin proteins can serve as potential exposure biomarkers. PMID:25778660

A kind of polarization beam splitter with triangular lattice of multi-walledcarbon nanotube arrays is designed and simulated. In the employed structure transverse-electric (TE) light is confined in the line defect with photonic band gap effect, while transverse-magnetic (TM) light is guided through it with extremely low diffraction. The performance of the designed polarization beam splitter is evaluated by utilizing optical properties of multi-walledcarbon nanotubes, finite element modeling of wave propagation and transmission through periodic arrays. Simulation results indicate that the designed polarization beam splitter has low loss and less cross talk, and thereby may have practical applications in the integrated optical field.

Buckling strengths, in terms of compressive strain, of single-, double- and triple-walled carbon nanotubes (CNTs) are investigated to study the effects of slenderness ratio ( SR) via the molecular dynamics (MD) simulations with the Tersoff potential. Under constant ratio of slenderness, the CNTs with small SR behave like a continuum shell object. For large SR's, multi-walled CNTs exhibit the characteristics of the Euler columns. In addition, smaller nanotubes possess higher buckling-resistance. The buckling strength of multi-walled nanotubes is controlled by the size of their outermost shell.

..., metal, glass, or ceramic form that is not intended to undergo further processing except for mechanical processing. (2) The significant new uses are: (i) Protection in the workplace. Requirements as specified in... 40 Protection of Environment 32 2013-07-01 2013-07-01 false Multi-walledcarbon nanotubes...

The high selectivity of the adsorption layer for low-boiling alkanes is shown, the separation factor (α) couple iso-butane / butane is 1.9 at a column temperature of 50 °C.The paper presents sorption and selective properties of planar gas chromatography column on aluminum plate with multi-walledcarbon nanotubes as the stationary phase.

Column experiments were conducted in undisturbed and in repacked soil columns at water contents close to saturation (85–96%) to investigate the transport and retention of functionalized 14C-labeled multi-walledcarbon nanotubes (MWCNT) in two natural soils. Additionally, a field lysimeter experiment...

... public comment period established in the Federal Register of February 3, 2010 (75 FR 5546) (FRL-8796-7... AGENCY 40 CFR Part 721 RIN 2070-AB27 Proposed Significant New Use Rule for Multi-walledCarbon Nanotubes... multi-walledcarbon nanotubes (P-08-199). In order to address public comments, EPA is adding...

The effect of pulsed ion irradiation and vacuum annealing on the ratio of sp 2- and sp 3-hybridized orbitals of carbon atoms in the layers of oriented multi-walledcarbon nanotubes has been studied by analyzing the photoemission spectra of the C1 s core level and the valence band of carbon, which were obtained using the equipment of the BESSY II Russian-German beamline of synchrotron radiation and a Riber analytical system. It has been shown that the ion irradiation leads to a significant decrease in the fraction of atoms with the sp 3 hybridization of electrons. On the contrary, the annealing reduces the fraction of the sp 3-component in the spectra of carbon. Typical features of the valence band of multi-walledcarbon nanotubes in the annealed and irradiated states have been established.

The tensile yielding of multiwall carbon nanotubes (MWCNTs) has been studied using Molecular Dynamics simulations and a Transition State Theory based model. We find a strong dependence of the yielding on the strain rate. A critical strain rate has been predicted above/below which yielding strain of a MWCNT is larger/smaller than that of the corresponding single-wall carbon nanotubes. At experimentally feasible strain rate of 1% /hour and T = 300K, the yield strain of a MWCNT is estimated to be about 3-4 % higher than that of an equivalent SWCNT (Single Wall Carbon Nanotube), in good agreement with recent experimental observations.

A multi-walledcarbon nanotube-based electrochemical biosensor is developed for monitoring microcystin-LR (MC-LR), a toxic cyanobacterial toxin, in sources of drinking water supplies. The biosensor electrodes are fabricated using dense, mm-long multi-walled CNT (MWCNT) arrays gro...

Reliable quantification techniques for carbon nanotubes (CNTs) are limited. In this study, a new procedure was developed for quantifying multi-walledcarbon nanotubes (MWNTs) in earthworms (Eisenia fetida) based on freeze drying and microwave-induced heating. Specifically, earthw...

A novel, cost-effective, easy and single-step process for the synthesis of large quantities of magnetic metal-encapsulated multi-walledcarbon nanobeads (MWNB) and multi-walledcarbon nanotubes (MWNT) using catalytic chemical vapour deposition of methane over Mischmetal-based AB3alloy hydride catalyst is presented. The growth mechanism of metal-encapsulated MWNB and MWNT has been discussed based on the catalytically controlled root-growth mode. These carbon nanostructures have been characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM and HRTEM), energy dispersive analysis of X-ray (EDAX) and thermogravimetric analysis (TGA). Magnetic properties of metal-filled nanobeads have been studied using PAR vibrating sample magnetometer up to a magnetic field of 10 kOe, and the results have been compared with those of metal-filled MWNT.

Forests of multi-walledcarbon nanotubes can be twisted and manipulated into continuous fibers or yarns that exhibit many of the characteristics of traditional textiles. Macro-scale analysis and test may provide strength and stiffness predictions for a composite composed of a polymer matrix and low-volume fraction yarns. However, due to the nano-scale of the carbon nanotubes, it is desirable to use atomistic calculations to consider tube-tube interactions and the influence of simulated twist on the effective friction coefficient. This paper reports laboratory test data on the mechanical response of a multi-walled, carbon nanotube yarn/polymer composite from both dynamic and quasi-static tensile tests. Macroscale and nano-scale analysis methods are explored and used to define some of the key structure-property relationships. The measured influence of hot-wet aging on the tensile properties is also reported.

The effects of surface modifications of multi-walledcarbon nanotubes (MWCNTs) on the morphology, dynamic mechanical and tribological properties of multi-walledcarbon nanotube/poly(ether ether ketone) (MWCNT/PEEK) composites have been investigated. MWCNTs were treated with mixed acids to obtain acid-functionalized MWCNTs. Then the acid-functionalized MWCNTs were modified with ethanolamine (named e-MWCNTs). The MWCNT/PEEK composites were prepared by a solution-blending method. A more homogeneous distribution of e-MWCNTs within the composites was found with scanning electron microscopy. Dynamic mechanical analysis demonstrated a clear increase in the storage modulus of e-MWCNT/PEEK composites because of the improved interfacial adhesion strength between e-MWCNTs and PEEK. Furthermore, the presence of e-MWCNTs caused an enhancement in the glass transition temperature of the composites. Wear tests have shown that the friction coefficient of e-MWCNT/PEEK composites decreased significantly during the test after the running-in period. This suggests that there is an obvious improvement in tribological properties of e-MWCNT/PEEK composites. Overall, the e-MWCNT/PEEK composites have exhibited improved properties and are promising for their applications in industry.

Linkage of proteins to carbon nanotubes (CNTs) is fundamentally important for applications of CNTs in medicinal and biological fields, as well as in biosensor or chemically modulated nanoelectronic devices. In this contribution, we provide a detailed protocol for the synthesis and characterization of covalent CNT-protein adducts. Functionalization of multiwalled carbon nanotubes (MWCNTs) with proteins has been achieved by the initial carboxylation of MWCNTs followed by amidation with the desired proteins. Attenuated total reflection Fourier transform infrared (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS) measurements validated the presence of a covalent linkage between MWCNTs and proteins. The visualization of proteins on the surface of MWCNTs was furthermore achieved using atomic force microscopy (AFM). The protein-conjugated nanocomposites can also be assembled into multidimensional addressable heterostructures through highly specific biomolecular recognition system (e.g., antibody-antigen). PMID:20422377

In this work, electrochemical properties of surface treated multi-walledcarbon nanotubes (MWNTs) are studied in supercapacitors. Nitrogen and oxygen functional groups containing MWNTs are prepared by urea and acidic treatments, respectively. The surface properties of the MWNTs are confirmed by X-ray photoelectron spectroscopy (XPS) and zeta-potential measurements. The textural properties are characterized by N{sub 2} adsorption/desorption isotherm at 77 K using the BET eqaution, BJH method, and HK method. The electrochemical properties of the MWNTs are accumulated by cyclic voltammetry, impedance spectra, and charge-discharge cycling performance in 1 M H{sub 2}SO{sub 4} at room temperature. As a result, the functionalized MWNTs lead to an increase in capacitance as compared with pristine MWNTs. It suggests that the pyridinic and pyridinic-N-oxides nitrogen species have effects on the specific capacitance due to the positive charge, and thus an improved electron transfer at high current loads results, the most important functional groups affecting capacitive behaviors. - Graphical Abstract: The N{sub 1s} spectra of nitrogen functionalized multi-walledcarbon nanotubes are measured by X-ray photoelectron spectroscopy. Highlights: > Facile method of increasing elemental composition of nitrogen functional groups on carbon materials. > Increased specific capacitance multi-walledcarbon nanotubes (MWNTs) for electrode materials as high as general chemical activation process. > Enhanced capacitive behaviors via introducing pyridinic and pyridinic-N-oxides nitrogen species onto the MWNTs. > Improvement of electron transfer at high current loads.

TiO2 particles coated Multi-walledcarbon nanotubes (MWCNT/TiO2 composite) were prepared via a sol-gel method using Multi-walledcarbon nanotubes (MWCNT) and tetrabutyl titanate as raw materials. The phase constitutes and microstructures of the prepared composite were analyzed by XRD and TEM, respectively. Their photocatalytic activities were investigated under simulated ultra-violet light and visible-light irradiation for the degradation of methyl orange (MO) and methylene blue (MB) aqueous solution, respectively. The experimental results indicated that TiO2 calcined at temperatures of 400-600 degrees C in the MWCNT/TiO2 composite was mainly composed of nanometric anatase. The composite exhibited enhanced absorption properties in the visible-light region compared to pure TiO2, which was attributed to the enhanced light electron-hole separation by adding MWCNTs. PMID:27455683

Multi-walledcarbon nanotubes (MWCNTs) were irradiated by Gamma (γ)-rays in air with absorbed doses of 25 and 50 kGy. As a result of γ-ray irradiation, the inter-wall distance of MWCNTs was decreased and their graphitic order was improved. The reduction in inter-wall distance and structural ordering was improved with the increasing dosage of irradiation. Experimental evidences are provided by powder XRD and micro-Raman analyses.

Despite voluminous research on the acid oxidation of carbon nanotubes (CNTs), there is a distinct lack of experimental results showing distributions of functional groups at the nanometre length scale. Here, functional peaks have been mapped across individual multi-walled CNTs with low-dose, monochromated electron energy-loss spectroscopy (EELS) in the scanning transmission electron microscope (STEM). Density functional theory simulations show that the EELS features are consistent with oxygenated functional groups, most likely carboxyl moieties. PMID:24827593

Nanocomposite of multi-walledcarbon nanotube@zeolite imidazolate frameworks (MWNT@ZIF) was prepared through a nanotube-facilitated growth based on a nanosized ZnO precursor. The electrically conductive nanocomposite displays a capacity of 380 mAh/g at 0.1 °C in Li–sulfur battery, transforming electrically inactive ZIF into the active one for battery applications.

Comprehensive investigations of aluminum nanopowders, multi-walledcarbon nanotubes, and aluminum mixtures with multi-walledcarbon nanotubes subjected to ultrasonic deagglomeration in a liquid medium were performed, using microstructural, X-ray diffraction, thermogravimetric, and calorimetric analyses, and specific surface area measurements. The regime of ultrasonic deagglomeration of aluminum nanopowders with multi-walledcarbon nanotubes in a liquid medium is described, during which the division of large agglomerates and creation of homogeneous distribution of mixtures components in the volume takes place. It was determined that ultrasonic treatment influences the morphology and crystalline structure of investigated mixtures, contributes to the appearance of X-ray amorphous phase, decreases the specific surface area of the aluminum nanopowder from 13 to 12 m{sup 2}/g, and increases the pore volume and average size from 0.04 to 0.06 cm{sup 3}/g and from 12 to 19 nm, respectively. The size of coherently-diffracting domain was determined by the X-ray diffraction analysis is close to that estimated from the specific surface area and corresponds to average crystallites size in the materials under study.

Multi-walledcarbon nanotubes were highly aggregated into ropes after their synthesis by chemical vapour deposition and, therefore, two different methods for disentangling the bundles of nanotubes were studied. One method compared the use of mild and vigorous mechanical treatments in ethanol and the other one employed dispersants in aqueous media. For comparison purposes and according to their different exfoliating behaviour, sodium dodecyl sulphate and gum arabic were selected as dispersants. The results evidenced that mechanical sonication was insufficient for disentangling the ropes, whereas, the combined action of mild sonication in an ultrasonic bath with the addition of gum arabic to an aqueous suspension containing nanotubes improved the exfoliating performance. Stable suspensions of unbundled multi-walledcarbon nanotubes were obtained adding only 0.05 wt% of gum arabic with a dispersant/MWNTs concentration ratio of 0.25. These values corresponded to a reduction in the dispersant concentration between 1 to 2 orders of magnitude compared to those commonly employed. In addition, a processing route for manufacturing dense and homogenous silicon nitride composites using spark plasma sintering with 1.8 vol% of multi-walledcarbon nanotubes almost free of organics was developed without nanotubes degradation and aggregation. PMID:19908510

Comprehensive investigations of aluminum nanopowders, multi-walledcarbon nanotubes, and aluminum mixtures with multi-walledcarbon nanotubes subjected to ultrasonic deagglomeration in a liquid medium were performed, using microstructural, X-ray diffraction, thermogravimetric, and calorimetric analyses, and specific surface area measurements. The regime of ultrasonic deagglomeration of aluminum nanopowders with multi-walledcarbon nanotubes in a liquid medium is described, during which the division of large agglomerates and creation of homogeneous distribution of mixtures components in the volume takes place. It was determined that ultrasonic treatment influences the morphology and crystalline structure of investigated mixtures, contributes to the appearance of X-ray amorphous phase, decreases the specific surface area of the aluminum nanopowder from 13 to 12 m2/g, and increases the pore volume and average size from 0.04 to 0.06 cm3/g and from 12 to 19 nm, respectively. The size of coherently-diffracting domain was determined by the X-ray diffraction analysis is close to that estimated from the specific surface area and corresponds to average crystallites size in the materials under study.

Nitrogen-doped multi-walledcarbon nanotubes (ND-MWCNTs) are modified multi-walledcarbon nanotubes (MWCNTs) with enhanced electrical properties that are used in a variety of applications, including fuel cells and sensors; however, the mode of toxic action of ND-MWCNT has yet to be fully elucidated. In the present study, we compared the interaction of ND-MWCNT or pristine MWCNT-7 with human small airway epithelial cells (SAEC) and evaluated their subsequent bioactive effects. Transmission electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and X-ray diffraction suggested the presence of N-containing defects in the lattice of the nanotube. The ND-MWCNTs were determined to be 93.3% carbon, 3.8% oxygen, and 2.9% nitrogen. A dose–response cell proliferation assay showed that low doses of ND-MWCNT (1.2 mg/ml) or MWCNT-7 (0.1 mg/ml) increased cellular proliferation, while the highest dose of 120 mg/ml of either material decreased proliferation. ND-MWCNT and MWCNT-7 appeared to interact with SAEC at 6 h and were internalized by 24 h. ROS were elevated at 6 and 24 h in ND-MWCNT exposed cells, but only at 6 h in MWCNT-7 exposed cells. Significant alterations to the cell cycle were observed in SAEC exposed to either 1.2 mg/ml of ND-MWCNT or MWCNT-7 in a time and material-dependent manner, possibly suggesting potential damage or alterations to cell cycle machinery. Our results indicate that ND-MWCNT induce effects in SAEC over a time and dose-related manner which differ from MWCNT-7. Therefore, the physicochemical characteristics of the materials appear to alter their biological effects. PMID:25797581

Recently, Geblinger et al. [Nat. Nanotechnol. 3, 195 (2008)] and Machado et al. [Phys. Rev. Lett. 110, 105502 (2013)] reported the experimental and molecular dynamics realization of S-like shaped single-walled carbon nanotubes (CNTs), the so-called CNT serpentines. We reported here results from continuum modeling of the binding energy γ between different single- and multi-walled CNT serpentines and substrates as well as the mechanical stability of the CNT serpentine formation. The critical length for the mechanical stability and adhesion of different CNT serpentines are determined in dependence of EiIi, d, and γ, where EiIi and d are the CNT bending stiffness and distance of the CNT translation period. Our continuum model is validated by comparing its solution to full-atom molecular dynamics calculations. The derived analytical solutions are of great importance for understanding the interaction mechanism between different single- and multi-walled CNT serpentines and substrates. PMID:24880308

In this Letter, we investigated the photo-response of multiwallcarbon nanotube-based composites obtained from in situ thermal evaporation of noble metals (Au, Ag, and Cu) on the nanotube films. The metal deposition process produced discrete nanoparticles on the nanotube outer walls. The nanoparticle-carbon nanotube films were characterized by photo-electrochemical measurements in a standard three electrode cell. The photocurrent from the decorated carbon nanotubes remarkably increased with respect to that of bare multiwall tubes. With the aid of first-principle calculations, these results are discussed in terms of metal nanoparticle-nanotube interactions and electronic charge transfer at the interface.

In this study, two enzyme electrodes based on graphene (GR), Co3O4 nanoparticles and chitosan (CS) or multi-walledcarbon nanotubes (MWCNTs), Co3O4 nanoparticles, and CS, were fabricated as novel biosensing platforms for galactose determination, and their performances were compared. Galactose oxidase (GaOx) was immobilized onto the electrode surfaces by crosslinking with glutaraldehyde. Optimum working conditions of the biosensors were investigated and the analytical performance of the biosensors was compared with respect to detection limit, linearity, repeatability, and stability. The MWCNTs-based galactose biosensor provided about 1.6-fold higher sensitivity than its graphene counterpart. Moreover, the linear working range and detection limit of the MWCNTs-based galactose biosensor was superior to the graphene-modified biosensor. The successful application of the purposed biosensors for galactose biosensing in human serum samples was also investigated. PMID:27074783

Iron oxide particles with the diameter being 5-10 nm were attached onto the sidewalls of multi-walledcarbon nanotubes (MWCNTs) by the thermal decomposition of cyclopentadieny iron (II) dicarbonyl dimmer. The red shift of G-mode from 1579 cm(-1) to 1571 cm(-1) in the Raman profile of the decorated MWCNTs is indicative of the attachment of nanoparticles. Electron energy loss spectroscopy and X-ray photoelectron spectroscopy analyses reveals that the attached nanoparticles are composed of a maghemite phase. Transmission electron microscopy suggests the maghemite particles are covered with amorphous carbon materials and form a core-shell structure. PMID:24374884

In this chapter, a multi-step protocol for covalently linking functionalized multi-walledcarbon nanotubes (MWCNT) to deoxyribonucleic acid (DNA) oligonucleotides is provided. X-ray photoelectron spectroscopy (XPS) is used to characterize the initially formed amine-terminated MWCNTs, to which DNA is covalently anchored. Atomic force microscopy (AFM) investigation of the DNA-MWCNT conjugates reveals that the chemical functionalization occurs at both the ends and sidewalls of the nanotubes. The described methodology represents an important step toward the realization of DNA-guided self-assembly for carbon nanotubes. PMID:20422378

Multi-walledcarbon nanotubes (MWNTs) have been reacted with 3,6-diaminotetrazine under heating. This process involves series of interactions between tetrazines and carbon nanotubes including π-π interactions, cycloaddition (Diels-Alder) and cross-linking reactions. These interactions resulted in coating of the MWNTs and in the formation of Y-junctions between nanotubes. Long heating (48 h) of MWNTs with the terazine resulted in a partial destruction of nanotubes due to their excessive functionalisation. The new nanocomposites have been studied by TEM, FTIR and Raman spectroscopy.

The poor dispersion of carbon based nanomaterials without strong acid pretreatment in aqueous solution is a fundamental problem, limiting its applications in biology-related fields. A good dispersion of multi-walledcarbon nanotubes (MWCNTs) in water was realized by 50 wt.% phytic acid (PA) solution. As an application case, the PA-MWCNTs dispersion in aqueous solution was used for the immobilization of horseradish peroxidase (HRP) and its direct electrochemistry was realized. The constructed biosensor has a sound limit of detection, wide linear range, and high affinity for hydrogen peroxide (H2O2) as well as being free from interference of co-existing electro-active species.

Carbon nanotubes (CNTs) possess high surface active site to volume ratio as well as controlled pore size distribution that make them high profile material with an exceptional sorption capability and high sorption efficiency compared to conventional adsorbents. In the present paper, multiwalledcarbon nanotubes were synthesized by chemical vapor deposition (CVD) method and were further used for the removal of dye crystal violet. Microscopic and spectroscopic techniques were used for characterization. The systematic assessments of the pH and effect of adsorbent on different concentrations of dye with respect to contact time were examined. Langmuir and Temkin models were used to describe the isotherm studies. PMID:25924370

Electromagnetic interference shielding properties of carbon nanofiber- and multi-walledcarbon nanotube-filled polystyrene composites were investigated in the frequency range of 8.2-12.4 GHz (X-band). It was observed that the shielding effectiveness of composites was frequency independent, and increased with the increase of carbon nanofiber or nanotube loading. At the same filler loading, multi-walledcarbon nanotube-filled polystyrene composites exhibited higher shielding effectiveness compared to those filled with carbon nanofibers. In particular, carbon nanotubes were more effective than nanofibers in providing high EMI shielding at low filler loadings. The experimental data showed that the shielding effectiveness of the composite containing 7 wt% carbon nanotubes could reach more than 26 dB, implying that such a composite can be used as a potential electromagnetic interference shielding material. The dominant shielding mechanism of carbon nanotube-filled polystyrene composites was also discussed. PMID:16060155

Well aligned, long and dense multi-walledcarbon nanotubes (CNT) can be grown on both carbon fibres and any metal substrates compatible with the CNT synthesis temperature. The injection-CVD process developed involves two stages, including fibre pretreatment by depositing a SiO(2)-based sub-layer from an organometallic precursor followed by CNT growth from toluene/ferrocene precursor mixture. Carbon substrates, as well as metals, can easily be treated with this process, which takes place in the same reactor and does not need any handling in between the two stages. The aligned CNT carpets obtained are similar to the ones grown on reference quartz substrates. The CNT growth rate is fairly high (ca. 30 μm min(-1)) and it is possible to control CNT length by varying the CNT synthesis duration. The thickness of the SiO(2)-based sub-layer can be varied and is shown to have an influence on the CNT growth. This layer is assumed to play a diffusion barrier layer role between the substrate and the iron based catalyst nanoparticles producing CNT. The CNT anchorage to the carbon fibres has been checked and good overall adhesion proved, which is in favour of a good transfer of electrical charge and heat between the nanotubes and fibre. PMID:22362164

Ionization gas sensors using vertically aligned multi-wallcarbon nanotubes (MWCNT) are demonstrated. The sharp tips of the nanotubes generate large non-uniform electric fields at relatively low applied voltage. The enhancement of the electric field results in field emission of electrons that dominates the breakdown mechanism in gas sensor with gap spacing below 14 μm. More than 90% reduction in breakdown voltage is observed for sensors with MWCNT and 7 μm gap spacing. Transition of breakdown mechanism, dominated by avalanche electrons to field emission electrons, as decreasing gap spacing is also observed and discussed.

Multi-walledcarbon nanotubes (MWCNTs) and graphite nanosheets (GNS) reinforced epoxy nanocomposites are synthesized by solution mixing process. Various surface active groups on filler materials are analyzed and their effect on dispersion, interfacial bonding was correlated to the thermal conductivity and dimensional stability of the nanocomposites. Thermal conductivity of MWCNTs/epoxy nanocomposites was enhanced by 34% when compared to GNS/epoxy nanocomposites at room temperature. Improved dimensional stability was also observed in the case of MWCNTs/epoxy nanocomposites. Poor thermal properties of GNS/epoxy nanocomposites are due to formation of GNS agglomerates in the nanocomposites.

A novel growth technique of boron-doped multi-walledcarbon nanotubes (MWNTs) was developed. Our new technique uses a methanol solution of boric acid as a source material. Resistivity of the boron-doped MWNTs was successfully reduced independently of chirality by our technique. Temperature dependence of resistivity in each individual boron-doped MWNT was measured by using small-sized four-point contacts, which were fabricated by electron beam (EB) lithography technique. Conduction carriers were introduced into the MWNT effectively by boron-doping.

Phonon confinement and in situ thermal conductance measurements in an individual multi-walledcarbon nanotube (MWNT) are reported. Focused ion beam (FIB) irradiation was used to successively shorten a 4.8 μm long MWNT, eventually yielding a 0.3 μm long MWNT. After the first FIB irradiation, a 41% reduction in conductance was achieved, compared with that of the pristine MWNT. This was because the contributions from phonons with long free paths were excluded by scattering at FIB-induced defects. Phonon transport in linked multiple-length nanotubes was also investigated.

We report on fabrication of an aluminum matrix composite containing multi-walledcarbon nanotubes (MWCNTs) produced by MOCVD method and functionalized via acid treatment by a H2SO4/HNO3 mixture. Specimens were prepared by spark plasma sintering (SPS) of the aluminum powder with different amounts of functionalized MWCNTs (FMWCNTs) in the range of 0.1-1 wt.%. We studied the effect of FMWCNTs amount on microstructure and mechanical properties of composites. It is shown that functionalization allows homogeneous dispersing of the MWCNTs in Al powder. The maximal increase in micro-hardness and tensile strength is registered at 0.1 wt.%.

Different types of multi-walledcarbon nanotubes (CNTs), synthesized by chemical vapor deposition, are used to fabricate infrared (IR) detectors on flexible substrates based on CNT p-n junctions. It is found that this kind of detector is sensitive to infrared signals with a power density as low as 90 μW mm(-2) even at room temperature. Besides, unlike other devices, the detector with this unique structure can be bent for 100 cycles without any damage and its functionality does not degenerate once it recovers to the initial state. The results give a good reference for developing efficient, low-cost, and flexible IR detectors. PMID:27101973

Zinc oxide (ZnO)/multiwalledcarbon nanotubes (MWCNTs) composites based sensors with different ZnO concentrations were fabricated to improve carbon monoxide (CO) gas sensing properties in comparison to the sensors based on bare MWCNTs. To study the structure, morphology and elemental composition of the resultant products, X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM) and Energy dispersive X-ray spectroscopy (EDS) were carried out. It has been observed that as the concentration of ZnO is increased more and more ZnO nanoparticles in the form of nodes get attached to MWCNTs resulting the reduction in average diameter of MWCNTs. The typical response of ZnO/MWCNTs composites based gas sensors for different CO concentrations (40, 100, 140 and 200 ppm) was studied by using very advanced sensing setup attached to I-V measurement system. Different sensing parameters such as: resistive response, sensitivity and response time were estimated at room temperature for all the fabricated sensors. The results indicated that the sensor based on nanocomposite which has 30 mg ZnO dispersed on 20 mg MWCNTs showing highest sensitivity and fastest response. All the sensors showed response times ranging from 8 to 23 seconds. The sensing mechanism behind the sensors based on ZnO/MWCNTs nanocomposites for CO gas at room temperature is also discussed in the present report. PMID:27398472

The nanocomposites of multi-walledcarbon nanotubes (MWNTs) decorated with nickel nanoparticles were conveniently prepared by a chemical reduction of nickel salt in the present of poly(acrylic acid) grafted MWNTs (PAA-g-MWNTs). Due to the strong interaction between Ni{sup 2+} and -COOH, PAA-g-MWNTs became an excellent supporting material for Ni nanoparticles. The morphology and distribution of Ni nanoparticles on the surface of MWNTs were greatly influenced by the reduction temperatures, the experimental results also showed that the distribution of Ni nanoparticles was greatly improved while the MWNTs were modified by poly(acrylic acid) (PAA). The hydrogenation activity and selectivity of MWNTs decorated with Ni nanoparticles (Ni-MWNTs) for alpha, beta-unsaturated aldehyde (citral) were also studied, and the experimental results showed that the citronellal, an important raw material for flavoring and perfumery industries, is the favorable product with a percentage as high as 86.9%, which is 7 times higher than that of catalyst by Ni-supported active carbon (Ni-AC). - Abstract: Nickel nanoparticles decorated multi-walledcarbon nanotubes (Ni-MWNTs) nanocomposites were conveniently prepared by a chemical reduction of nickel salt in the present of poly(acrylic acid) grafted MWNTs (PAA-g-MWNTs). These nanocomposites possessed excellent catalytic activity and selectivity for hydrogenation of citral.

Method and system for producing a selected pattern or array of at least one of a single wall nanotube and/or a multi-wall nanotube containing primarily carbon. A substrate is coated with a first layer (optional) of a first selected metal (e.g., Al and/or Ir) and with a second layer of a catalyst (e.g., Fe, Co, Ni and/or Mo), having selected first and second layer thicknesses provided by ion sputtering, arc discharge, laser ablation, evaporation or CVD. The first layer and/or the second layer may be formed in a desired non-uniform pattern, using a mask with suitable aperture(s), to promote growth of carbon nanotubes in a corresponding pattern. A selected heated feed gas (primarily CH4 or C2Hn with n=2 and/or 4) is passed over the coated substrate and forms primarily single wall nanotubes or multiple wall nanotubes, depending upon the selected feed gas and its temperature. Nanofibers, as well as single wall and multi-wall nanotubes, are produced using plasma-aided growth from the second (catalyst) layer. An overcoating of a selected metal or alloy can be deposited, over the second layer, to provide a coating for the carbon nanotubes grown in this manner.

The temperature dependent conductivity of multi-walledcarbon nanotube film (MWNT) is reported and the different electrical properties of nanotubes in two composites are compared. Due to the disordered structures, our carbon nanotube film displays variable range hopping behavior. While the geometric distributions of carbon nanotubes in the conducting polyaniline (PANI) and insulating polyamide (PA66) are similar, charge carriers transport distinctly. The conductive PANI, following one-dimensional variable range hopping, dominates the electrical properties of MWNT/PANI composites. The effect of MWNTs becomes prominent only at low temperature range. However, the contact junctions composed by adjacent carbon nanotubes, instead of nanotubes themselves or the polymer matrix, determine the electrical properties of MWNT/PA66 composites, showing the fluctuation induced tunneling characteristic.

Polyaniline/multi-walledcarbon nanotube composites (PANI/MWCNT), with various concentration of multi-walledcarbon nanotube, were synthesized. Several Schottky diodes were fabricated, where PANI or PANI/MWCNT composites, aluminum, and gold were used as semiconductor, Schottky contact, and ohmic contact, respectively. Then current-voltage characteristics of the fabricated diodes were measured at room temperature and within the bias range of -5 to +5 V. The measurements were repeated three times for each sample to verify repeatability of experiment. The obtained results show that by increasing the MWCNT concentration, the current intensity increases. Furthermore, I-V characteristics of pure polyaniline Schottky diode follows the thermionic emission mechanism while the I-V characteristics of Schottky diodes based on PANI/MWCNT composites show two distinct power law regions. At lower voltages, the mechanism follows Ohm's Law, whereas at higher voltages, the mechanism is compatible with space charge limited conduction emission mechanism. The parameters of Schottky diodes were determined, and it was observed that critical voltage decreased when the concentration of MWCNT in the composite increased.

Different types of multi-walledcarbon nanotubes (CNTs), synthesized by chemical vapor deposition, are used to fabricate infrared (IR) detectors on flexible substrates based on CNT p-n junctions. It is found that this kind of detector is sensitive to infrared signals with a power density as low as 90 μW mm-2 even at room temperature. Besides, unlike other devices, the detector with this unique structure can be bent for 100 cycles without any damage and its functionality does not degenerate once it recovers to the initial state. The results give a good reference for developing efficient, low-cost, and flexible IR detectors.Different types of multi-walledcarbon nanotubes (CNTs), synthesized by chemical vapor deposition, are used to fabricate infrared (IR) detectors on flexible substrates based on CNT p-n junctions. It is found that this kind of detector is sensitive to infrared signals with a power density as low as 90 μW mm-2 even at room temperature. Besides, unlike other devices, the detector with this unique structure can be bent for 100 cycles without any damage and its functionality does not degenerate once it recovers to the initial state. The results give a good reference for developing efficient, low-cost, and flexible IR detectors. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr08791k

A rapid microwave-assisted method was developed for the purification, cutting and unzipping of arrays of multi-walledcarbon nanotubes (MWCNTs) using a mixture of KMnO4 and H2SO4. To harness the extent of treatment, MWCNT products were fully characterized at different reaction times by UV-visible and Raman spectroscopies as well as scanning and transmission electron microscopies. The results show that the carbon nanoparticles and the amorphous carbon which coated the MWCNTs were removed after about 10 minutes. The excessive oxidation of MWCNTs then leads to cutting and unzipping of graphitic walls. Moreover, while the catalyst residues outside the MWCNTs were rapidly extracted up to 10 minutes, the removal of catalyst residues inside the MWCNTs did not begin before 20 minutes. This method can be considered as an efficient route for the purification, cutting and unzipping of MWCNTs due to its fast and controllable procedure.

We performed simultaneous Raman spectroscopy and electrical conductivity measurements on self-standing aligned multi-walledcarbon nanotubes sheets at varying inter-tube distances. A sapphire anvil cell is used here to modulate the inter-tube distance and promote the subsequent electronic tunneling phenomena. We observe a singular correlation between the intensity of the so called defect bands of carbon materials and their conductivity. This indicates that the conditions of the resonant processes that originate these bands are modified by the tunneling phenomena. Such an issue has never been reported before and has potential technological applications. Additionally, the provided AFM images evidence the debundling of the carbon nanotubes that had been described to occur after small compression.

This work investigates the reflection and scattering from vertically aligned carbon nanotubes, fabricated on silicon substrate using thermally enhanced chemical vapor deposition with both tip-growth and base-growth mechanisms. The directional-hemispherical reflectance in the visible and near-infrared wavelengths was measured with an integrating sphere. The polarization-dependent bidirectional reflectance distribution function was characterized with a laser scatterometer at the wavelength of 635 nm. The effective medium theory was used to elucidate the mechanism of high absorptance (greater than 0.97 in the spectral region from 400 to 1800 nm) of the multi-walledcarbon nanotube samples. It is observed that scattering by impurities on the top of the nanotubes, by the nanotube tips, and by defects and misalignment can significantly increase the reflectance and introduce retroreflection. This study may facilitate application of carbon nanotubes in pyroelectric detectors as well as thermophotovoltaic emitters and absorbers. PMID:19423943

Recently, Geblinger et al. [Nat. Nanotechnol. 3, 195 (2008)] and Machado et al. [Phys. Rev. Lett. 110, 105502 (2013)] reported the experimental and molecular dynamics realization of S-like shaped single-walled carbon nanotubes (CNTs), the so-called CNT serpentines. We reported here results from continuum modeling of the binding energy γ between different single- and multi-walled CNT serpentines and substrates as well as the mechanical stability of the CNT serpentine formation. The critical length for the mechanical stability and adhesion of different CNT serpentines are determined in dependence of E{sub i}I{sub i}, d, and γ, where E{sub i}I{sub i} and d are the CNT bending stiffness and distance of the CNT translation period. Our continuum model is validated by comparing its solution to full-atom molecular dynamics calculations. The derived analytical solutions are of great importance for understanding the interaction mechanism between different single- and multi-walled CNT serpentines and substrates.

Synthetic methodology and characterization of multi-walledcarbon nanotubes (MWCNTs) function- alized with hydroxymethylene groups are reported. The MWCNTs were synthesized by the spray pyrolysis technique using toluene as carbon source and ferrocene as catalyst. Hydroxymethylation of MWCNTs was carried out by methanol using benzoyl peroxide (BPO) at different quantities (300 to 900 mg); the optimum BPO quantity was 300 mg. The resulting materials were characterized by FT-IR, Raman Spectroscopy, Thermal Gravimetric Analysis (TGA) and Transmission Electron Microscopy (TEM). The presence of the hydroxymethylene group on the MWCNTs surface was demonstrated by FT-IR, Raman Spectroscopy, TGA, EDS, TEM and Mass Spectrometry. The func- tionalized MWCNTs were not damaged by this methodology. PMID:27398563

Large-scale graphene or carbon nanotube (CNT) films are good candidates for transparent flexible electrodes, and the strong interest in graphene and CNT films has motivated the scalable production of a good-conductivity and an optically transmitting film. Unzipping techniques for converting CNTs to graphene are especially worthy of notice. Here, we performed nanotube unzipping of the spun multi-walledcarbon nanotubes (MWCNTs) to produce networked graphene nanoribbon (GNR) sheet films using an 02 plasma etching method, after which we produced the spun MWCNT film by continually pulling MWCNTs down from the vertical well aligned MWCNTs on the substrate. The electrical resistance was slightly decreased and the optical transmittance was significantly increased when the spun MWCNT films were etched for 20 min by O2 plasma of 100 mA. Plasma etching for the optimized time, which does not change the thickness of the spun MWCNT films, improved the electrical resistance and the optical transmittance. PMID:26726645

We report magnetic measurements up to 1200 K on multi-walledcarbon nanotube mats using a Quantum Design vibrating sample magnetometer. Extensive magnetic data consistently show two ferrromagnetic-like transitions at about 1000 K and 1275 K, respectively. The lower transition at about 1000 K is associated with an Fe impurity and its saturation magnetization is in quantitative agreement with the Fe concentration measured from an inductively coupled plasma mass spectrometer. On the other hand, the saturation magnetization for the higher transition phase corresponds to about 0.6% Co impurity concentration, which is about four orders of magnitude larger than that measured from the mass spectrometer. We show that this transition at about 1275 K is not consistent with ferromagnetism of any carbon-based phases or magnetic impurities but with the paramagnetic Meissner effect due to the existence of π Josephson junctions in a granular superconductor.

Metal matrix composites (MMCs) reinforced with ceramic nano particles (less than 100 nm), termed as metal matrix nano composites (MMNCs), can overcome those disadvantages associated with the conventional MMCs. MMCs containing carbon nanotubes are being developed and projected for diverse applications in various fields of engineering like automotive, avionic, electronic and bio-medical sectors. The present investigation deals with the synthesis and characterization of hybrid magnesium matrix reinforced with various different wt% (0-0.45) of multiwallcarbon nano tubes (MWCNT) and micro SiC particles prepared through powder metallurgy route. Microstructure and mechanical properties such as micro hardness and density of the composites were examined. Microstructure of MMNCs have been investigated by scanning electron microscope, X-ray diffraction and energy dispersive X-ray spectroscopy (EDS) for better observation of dispersion of reinforcement. The results indicated that the increase in wt% of MWCNT improves the mechanical properties of the composite.

A microstructure, a composition and mechanical properties of multi-walledcarbon of nanotube-reinforced silicon carbide ceramics were examined. The amount of carbon nanotubes was up to 1% wt. Samples was prepared by spark plasma sintering. It has been found that the optimal sintering temperature is 2000°C with an exposure duration of 5 minutes and a pressure of 50 MPa. The effect of the CNT mass fraction on the Young modulus of silicon carbide ceramics composites was investigated for different temperatures and processing conditions of samples using ultrasonic techniques. It has been established that Young's modulus of ceramics decreases due to addition of CNT. Elastic properties of the composites cross section were characterized using nano-indentation. It has been revealed that the stiffness of the ceramics intergranular phase decreases due to addition of CNT.

We report on the increase of the Young's modulus (E) of chemical vapor deposition (CVD) grown multi-walledcarbon nanotubes (MWNTs) upon high temperature heat treatment. The post heat-treatment at 2200-2800°C in a controlled atmosphere results in a considerable improvement of the microstructure, chemical stability and electro-physical properties of the nanotubes. The Young's modulus of MWNTs of different diameters was measured by the deflection of a single tube suspended across the hole of silicon nitride membrane and loaded by an atomic force microscope tip. Contrary to previous reports, a strong increase of E was feasible due to the improved growth conditions of pristine carbon nanotubes and to the improved heat treatment conditions. However, the elastic modulus of CVD grown MWNTs still shows strong diameter dependence resulting from the remaining structural inhomogeneities in large diameter nanotubes.

Evaporation and condensation of water on multi-walledcarbon nanotube (MWCNT) surfaces was monitored as a function of both temperature and time using x-ray Spatial Frequency Heterodyne Imaging (SFHI). SFHI is an imaging method that produces an absorption and scatter image from a single exposure, with increased sensitivity to variations in electron density relative to more common place x-ray imaging techniques. Different features seen in the temporal scatter intensity profiles recorded during evaporation and condensation revealed the existence of an absorption-desorption hysteresis. Effects on the previously mentioned phenomena due to chemical functionalization of the carbon nanotube surfaces were also observed. Functionalization increased the interaction potential between the MWCNT walls and water molecules, altering the evaporation event time scale and increasing the temperature at which condensation could take place. The observed temperature dependent changes in evaporation time scales coincide with the boiling point for confined water predicted by the Kelvin equation.

Catalytic chemical vapor deposition was used to grow multi-walledcarbon nanotubes on a Fe:Co:CaCO3 catalyst from acetylene. The influent and effluent gases were analyzed by gas chromatography and mass spectrometry at different time intervals during the nanotubes growth process in order to better understand and optimize the overall reaction. A large number of byproducts were identified and it was found that the number and the level for some of the carbon byproducts significantly increased over time. The CaCO3 catalytic support thermally decomposed into CaO and CO2 resulting in a mixture of two catalysts for growing the nanotubes, which were found to have outer diameters belonging to two main groups 8 to 35 nm and 40 to 60 nm, respectively.

Multi-wallcarbon nanotubes (MWCNTs) were synthesized by thermal chemical vapor deposition (CVD) and were intercalated with iodine at several different temperatures. Iodine doping was achieved by immersing the nanotubes in molten iodine. The sample produced was characterized by means of infrared IR as a point to the presence of covalent C-I bonds in the sample with retention of the sp{sup 2}-hybridizated carbon atoms. For all samples doped at different temperatures, the C-I bonding happen to occur based on IR spectra which was indicated by peaks around 600-650 cm{sup -1}. X-ray diffraction (XRD) characterization was used to study on the crystallinity of the undoped and iodine-doped MWCNTs. It was shown that, iodine-doping of the MWCNTs gives significant changes in the XRD spectra compared to the undoped MWCNTs. With various doping temperature, the XRD spectra shows the different crystallinity.

A comparative study on the sodium-ion insertion and extraction of commercially-available multi-wall and single-wall carbon nanotubes is reported. Single-wall carbon nanotubes exhibit charge/discharge capacities of 126 mA h g-1 and multi-wallcarbon nanotubes produce a lower capacity of 28 mA h g-1 after 50 cycles at 25 mA g-1. To understand these differences, a combination of X-ray diffraction and solid state nuclear magnetic resonance measurements were performed at various states of sodium insertion and extraction.23Na nuclear magnetic resonance studies, a technique previously rarely used for characterising electrodes from sodium-ion batteries, shows differences in the sodium chemical environment near multi-wall compared to single-wall carbon nanotubes with distinct sodium sites found to be active during sodium insertion and extraction for the carbon nanotubes. Both types of carbon nanotubes show a similar amount of reversible sodium available for insertion/extraction reactions, but multi-wallcarbon nanotubes feature half the initial insertion capacity relative to single-wall carbon nanotubes. The electrochemical performance of the carbon nanotube electrodes are discussed in relation to the observed mechanism of sodium insertion.

Increasing application of carbon nanotubes (CNTs) triggers the need for an assessment of their effects on organisms in the environment. Soil microbial communities play a significant role in soil organic matter dynamics and nutrient cycling. This study evaluated the impacts of multi-walledcarbon nan...

Nanotechnology offers the promise of creating new materials with enhanced performance. There are different kinds of fillers used in rubber nanocomposites, such as carbon black, silica, carbon fibers, and organoclays. Carbon nanotube reinforced elastomers have potential for improved rubber properties in aggressive environments. The first chapter is an introduction to the literature. The second chapter investigated the incorporation of multi-walledcarbon nanotubes (MWCNTs) into rubber matrix for potential use in high temperature applications. The vulcanization kinetics of acrylonitrile butadiene rubber (NBR) reinforced with multi-walledcarbon nanotubes was investigated. The vulcanized NBR rubber with different loading percentages of MWCNTs was also compared to NBR reinforced with carbon black N330. The optimum curing time at 170°C (T90) was found to decrease with increasing content of MWCNTs. Increased filler loading of both carbon black and MWCNTs gave higher modulus and strength. The MWCNTs filled materials gave better retention of modulus and tensile strength at high temperatures, but lower strength as compared to the carbon black filled samples. In the third chapter, carbon black (CB, 50phr) content in nitrile rubber (NBR) nanocomposites was partially replaced by multi-walledcarbon nanotubes (MWCNTs). NBR/CB/CNTs nanocomposites with varying ratio of CB/CNTs (50/0 phr to 40/10 phr) were formulated via the melt-mixing method using an internal mixer. The reinforcing effect of single filler (CB) and mixture of fillers (CB and CNTs) on the properties of NBR nanocomposites was investigated. The cure kinetics and bound rubber content were analyzed using rheometry and solvent swelling method. In addition, mechanical behavior at both room temperature and high temperature (350°F/ 121°C) were examined. The scorch time and curing time values showed that there was no significant effect on the curing behavior of NBR nanocomposites after the partial replacement of CB with

In the present study, multiwalledcarbon nano tubes (MWCNTs) were synthesized using chemical vapour deposition (CVD) technique. Swiss albino mice were orally administered with single dose of 60 and 100 mg/kg body weight of purified and functionalized MWCNTs suspended in water. The mice were autopsied on 7, 14, 21 and 28 days post exposure. Liver was taken out and part of it fixed in Bouin's solution for histopathological examinations. The remaining part was immersed in cold saline, blotted dry, weighed quickly and homogenized in ice cold buffer. The activity of superoxide dismutase (SOD) and catalase (CAT) was immediately measured in the supernatant. The MWCNTs in liver led to pathological changes, including injury to macrophages, cellular swelling, unspecific inflammation, spot necrosis and blood coagulation. Estimation of SOD and CAT showed altered levels in the experimental groups as compared to controls. Therefore, MWCNTs from manufactured and combustion sources in the environment can have adverse effects on human health. PMID:23000350

The nanocomposites of monodisperse polystyrene (PS) particles and multi-walledcarbon nanotubes (MWNTs) were prepared by latex technology to provide good dispersion of nanotubes in polymer matrix. Two kinds of monodisperse PS particles were synthesized either by emulsion polymerization or by dispersion polymerization. The MWNTs were dispersed in deionized water and mixed with the PS particles, and then PS/MWNT nanocomposites were prepared by freeze-drying and subsequent compression molding. Rheological and electrical properties of these nanocomposites were investigated. Pronounced effect of MWNT incorporation was observed, resulting in larger modulus at lower frequencies when compared to neat PS. The nanocomposite prepared under ultrasonication showed the optimum results providing good dispersion of MWNTs and high electrical conductivity. The effect of PS particle size on electrical conductivity was found to be dependent on the MWNT content incorporated.

Graphene quantum dots (GQDs), which are edge-bound nanometer-size graphene pieces, have fascinating electronic and optical properties due to their quantum confinement and edge effect. In this paper, GQDs were synthesized by using acid treatment and chemical exfoliation of multi-walledcarbon nanotubes (MWCNTs). The structure of the GQDs was investigated by transmission electron microscope. The GQDs have a uniform size distribution, zigzag edge structure and two-dimensional morphology. The results indicated that the GQDs have bright blue emission upon UV excitation. The highly fluorescent GQDs exhibited high water solubility and good stability. It is shown that the acid treatment of MWCNTs leads to the formation of the functional group in zigzag sites, which results in the pH-dependent fluorescence of the GQDs.

In order to examine the influence of multiwalledcarbon nanotube (MWNT) on physical properties of its biodegradable polymer nanocomposite, biodegradable poly(buthylene succinate) (PBS), which was synthesized from diols and dicarboxylic acids, and MWNT nanocomposites were prepared via a melt-mixing method using a co-rotating intermeshing twin screw extruder. Microstructure of the PBS/MWNT nanocomposites and MWNT were investigated via both scanning electron microscopy and transmission electron microscopy. Their rheological properties were also characterized via rotation and oscillation tests using a rotational rheometer with parallel-plate geometry. It was found that shear viscosity, storage modulus and loss modulus of the nanocomposites examined by a rotational rheometer increased with the MWNT content. Especially their sharp increase for MWNT content of ca. 2.0 wt% was observed, indicating its percolation threshold from the rheological viewpoint which was higher than its electrical percolation threshold (1.0 wt%). PMID:21770188

A facile approach to fabricate a stable superhydrophobic composite comprising multi-walledcarbon nanotubes and silicone rubber has been reported. Contact angle of de-ionized water droplets on the prepared surface was measured with the value of near 159°; while water droplets easily rolled off and bounced on it. Surface free energy of the superhydrophobic coating was examined by three methods about 26 mJ/m2. The prepared film shows good stability under high stress conditions such as ultraviolet exposure, heating, pencil hardness test, attacking with different pH value and ionic-strength solutions. In addition, remarkable stability of the coating was observed after soaking in condensed hydrochloric acid, 5 wt.% NaCl aqueous solution, boiling water and tape test.

The inclusion of nanoparticles modifies a number of fundamental properties of many materials. Doping of nanoparticles in self-organized materials such as liquid crystals may be of interest for the reciprocal interaction between the matrix and the nanoparticles. Elongated nanoparticles and nanotubes can be aligned and reoriented by the liquid crystal, inducing noticeable changes in their optical and electrical properties. In this work, cells of liquid crystal doped with high aspect ratio multi-walledcarbon nanotubes have been prepared, and their characteristic impedance has been studied at different frequencies and excitation voltages. The results demonstrate alterations in the anisotropic conductivity of the samples with the applied electric field, which can be followed by monitoring the impedance evolution with the excitation voltage. Results are consistent with a possible electric contact between the coated substrates of the LC cell caused by the reorientation of the nanotubes. The reversibility of the doped system upon removal of the electric field is quite low. PMID:25821679

In this study, laser-processed multi-walledcarbon nanotube (MWCNT)/Cu conductors are introduced as potential passive components to mitigate the skin effect of Cu at high frequencies (0–10 MHz). Suppressed skin effect is observed in the MWCNT/Cu conductors compared to primitive Cu. At an AC frequency of 10 MHz, a maximum AC resistance reduction of 94% was observed in a MWCNT/Cu conductor after being irradiated at a laser power density of 189 W/cm{sup 2}. The reduced skin effect in the MWCNT/Cu conductors is ascribed to the presence of MWCNT channels which are insensitive to AC frequencies. The laser irradiation process is observed to play a crucial role in reducing contact resistance at the MWCNT-Cu interfaces, removing impurities in MWCNTs, and densifying MWCNT films.

Abundant experimental data have shown that multi-walledcarbon nanotubes (MWNTs) are toxic to plants, but the potential impacts of exposure remain unclear. The objective of the present study was to evaluate possible phytotoxicity of MWNTs at 0, 20, 200, 1000, and 2000 mg/L with red spinach, lettuce, rice, cucumber, chili, lady's finger, and soybean based on root and shoot growth, cell death, and electrolyte leakage at the seedling stage. After 15 days of hydroponic culture, the root and shoot lengths of red spinach, lettuce, and cucumber were significantly reduced following exposure to 1000 mg/L and 2000 mg/L MWNTs. Similar toxic effects occurred regarding cell death and electrolyte leakage. Red spinach and lettuce were most sensitive to MWNTs, followed by rice and cucumber. Very little or no toxic effects were observed for chili, lady's finger, and soybean.

Laser irradiation of randomly oriented multi-walledcarbon nanotube (MWCNT) networks has been carried out using a pulsed Nd:YAG UV laser in nitrogen gas environment. The evolution of the MWCNT morphology and structure as a function of laser fluence and number of accumulated laser pulses has been studied using electron microscopies and Raman spectroscopy. The observed changes are discussed and correlated with thermal simulations. The obtained results indicate that laser irradiation induces very fast, high temperature thermal cycles in MWCNTs which produce the formation of different nanocarbon forms, such as nanodiamonds. Premelting processes have been observed in localized sites by irradiation at low number of laser pulses and low fluence values. The accumulation of laser pulses and the increase in the fluence cause the full melting and amorphization of MWCNTs. The observed structural changes differ from that of conventional high temperature annealing treatments of MWCNTs.

Functionalization is the process of introducing chemical functional groups on the surface of the material. In this study, a multi-walledcarbon nanotube (MWCNTs) was functionalized by oxidation treatment using concentrated nitric acid. The functionalized and pristine MWCNTs were analyzed by using Fourier Transform Infrared Spectroscopy (FT-IR) and X-Ray Diffraction (XRD). The XRD patterns exhibit the graphitic properties for all samples. Besides, the XRD results also demonstrate that the percent of crystallinity of MWCNTs increases as the duration of acid treatment increases. The percent of crystallinity increases from 66% to 80% when the pristine MWCNT treated for 12 hours with additional 12 hours reflux process with nitric acid. The IR spectrum for the 12 hours-treated MWCNTs shows the formation of carboxyl functional group. Additional 12 hours reflux process with nitric acid on the 12 hours-treated MWCNTs have shown the loss of existing carboxyl group and only hydroxyl group formed.

Porous polyaniline (PANI)-coated multi-walledcarbon nanotube (MWNT) core/shell nanohybrids were fabricated through in situ polymerization and subsequently assembled into macroscopic composites. N(2) adsorption/desorption analysis indicated that the volume of nanopores increased significantly, which could make a significant contribution to phonon scattering. Thermal annealing was also carried out to improve the Seebeck coefficient of the as-produced nanocomposites. The optimal sample showed electrical conductivity of 14.1 S cm(-1), a Seebeck coefficient of 79.8 μV K(-1) and thermal conductivity of 0.27 W mK(-1), resulting in a highest figure of merit (ZT) of 0.01 at a very low loading of MWNTs (<1 wt%). These results will provide a potential direction to enhance thermoelectric performance of organic materials and also facilitate the application of organic materials in thermal energy harvesting or cooling. PMID:22947620

Porous polyaniline (PANI)-coated multi-walledcarbon nanotube (MWNT) core/shell nanohybrids were fabricated through in situ polymerization and subsequently assembled into macroscopic composites. N2 adsorption/desorption analysis indicated that the volume of nanopores increased significantly, which could make a significant contribution to phonon scattering. Thermal annealing was also carried out to improve the Seebeck coefficient of the as-produced nanocomposites. The optimal sample showed electrical conductivity of 14.1 S cm-1, a Seebeck coefficient of 79.8 μV K-1 and thermal conductivity of 0.27 W mK-1, resulting in a highest figure of merit (ZT) of 0.01 at a very low loading of MWNTs (<1 wt%). These results will provide a potential direction to enhance thermoelectric performance of organic materials and also facilitate the application of organic materials in thermal energy harvesting or cooling.

Functionalization is the process of introducing chemical functional groups on the surface of the material. In this study, a multi-walledcarbon nanotube (MWCNTs) was functionalized by oxidation treatment using concentrated nitric acid. The functionalized and pristine MWCNTs were analyzed by using Fourier Transform Infrared Spectroscopy (FT-IR) and X-Ray Diffraction (XRD). The XRD patterns exhibit the graphitic properties for all samples. Besides, the XRD results also demonstrate that the percent of crystallinity of MWCNTs increases as the duration of acid treatment increases. The percent of crystallinity increases from 66% to 80% when the pristine MWCNT treated for 12 hours with additional 12 hours reflux process with nitric acid. The IR spectrum for the 12 hours-treated MWCNTs shows the formation of carboxyl functional group. Additional 12 hours reflux process with nitric acid on the 12 hours-treated MWCNTs have shown the loss of existing carboxyl group and only hydroxyl group formed.

In this paper the polymer nanocomposite of multi-walledcarbon nanotubes (MWCNTs) nanoparticles was incorporated with polylactic acid (PLA) and liquid natural rubber (LNR) as compatibilizer were prepared via melt blending method. The effect of MWCNTs loading on the tensile and impact properties of nanocomposites was investigated. The result has shown that the sample with 3.5 wt % of MWCNTs exhibited higher tensile strength, Young's modulus and impact strength. The elongation at break decreased with increasing percentage of MWCNTs. The SEM micrographs confirmed the effect of good dispersion of MWCNTs and their interfacial bonding in PLA/LNR composites. The improved dispersion of MWCNTs can be obtained due to altered interparticle interactions, MWCNTs-MWCNTs and MWCNTs-matrix networks are well combined to generate the synergistic effect of the system as shown by SEM micrographs which is improved the properties significantly.

In this study, nanoscale welding quality and morphology changes of multi-walledcarbon nanotubes are investigated by changing laser wavelengths and the irradiation time. Lasers with 1064 nm and 355 nm are used in our experiments. The 1064 nm laser can lead to nanowelding with good quality, while the 355 nm laser changes the curvature. The experiments demonstrate that the morphology, structures and the welding quality can be adjusted by changing laser wavelengths. In this letter, the dynamic process of nanostructures changing is studied by changing the irradiation time. The experimental results show that the morphology and structures can be controlled by adjusting the irradiation time. The detailed dynamic process of nanostructures changing confirms the formation mechanism of nano-welding and the thermal effects during the process.

We studied the effects of multi-walledcarbon nanotubes (MWCNTs) on the electrophysiological properties of cultured mouse chromaffin cells, a model of spontaneously firing cells. The exposure of chromaffin cells to MWCNTs at increasing concentrations (30-263 μg/ml) for 24 h reduced, in a dose-dependent way, both the cell membrane input resistance and the number of spontaneously active cells (from 80-52%). Active cells that survived from the toxic effects of MWCNTs exhibited more positive resting potentials, higher firing frequencies and unaltered voltage-gated Ca(2+), Na(+) and K+ current amplitudes. MWCNTs slowed down the inactivation kinetics of Ca(2+)-dependent BK channels. These electrophysiological effects were accompanied by MWCNTs internalization, as confirmed by transmission electron microscopy, indicating that most of the toxic effects derive from a dose-dependent MWCNTs-cell interaction that damages the spontaneous cell activity. PMID:21322767

Multi-walledcarbon nanotubes (MWCNTs) are grown by arc discharge method in a controlled methane environment. The arc discharge is produced between two graphite electrodes at the ambient pressures of 100 torr, 300 torr, and 500 torr. Arc plasma parameters such as temperature and density are estimated to investigate the influences of the ambient pressure and the contributions of the ambient pressure to the growth and the structure of the nanotubes. The plasma temperature and density are observed to increase with the increase in the methane ambient pressure. The samples of MWCNT synthesized at different ambient pressures are analyzed using transmission electron microscopy, scanning electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, and X-ray diffraction. An increase in the growth of MWCNT and a decrease in the inner tube diameter are observed with the increase in the methane ambient pressure.

We perform large-scale quasi-continuum simulations to determine the stable cross-sectional configurations of free-standing multi-walledcarbon nanotubes (MWCNTs). We show that at an inter-wall spacing larger than the equilibrium distance set by the inter-wall van der Waals (vdW) interactions, the initial circular cross-sections of the MWCNTs are transformed into symmetric polygonal shapes or asymmetric water-drop-like shapes. Our simulations also show that removing several innermost walls causes even more drastic cross-sectional polygonization of the MWCNTs. The predicted cross-sectional configurations agree with prior experimental observations. We attribute the radial corrugations to the compressive stresses induced by the excessive inter-wall vdW energy release of the MWCNTs. The stable cross-sectional configurations provide fundamental guidance to the design of single MWCNT-based devices and shed lights on the mechanical control of electrical properties.

Regenerated cellulose (RC)-based composites reinforced with multi-walledcarbon nanotubes (MWCNTs) were prepared by a facile casting method. The morphology and microstructure of the fabricated composites were characterized using transmission electron microscopy, Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. Thermogravimetry and derivative thermogravimetric analysis were conducted to investigate the effect of MWCNTs on the thermal behaviors of the RC. The results showed that the introduction of MWCNTs enhanced the thermal stability of the RC. Moreover, the effect of the dispersion state of MWCNTs in microcrystalline cellulose/ZnCl2 solutions with varying MWCNT loadings was studied by rheological tests. The mechanical properties of composite films were remarkably improved compared to those of pure RC film. Specifically, the composite film containing 3 wt% of MWCNTs exhibits a 123% enhancement in tensile strength and a 163% enhancement in the Young's modulus compared with the pure RC film. PMID:27574002

Chemical vapor deposition (CVD) was optimized in order to prepare multi-wallcarbon nanotubes (MWCNTs). Preparation of MWCNTs was achieved by the help of ferrocene as a catalyst with continuous flow of xylene. Morphology and structure of as grown and purified MWCNTs were characterized by Scanning Electron Microscope (SEM) and High-Resolution Transmission Electron Microscope (HRTEM). Energy Dispersive X-ray (EDX) spectra for the as grown MWCNTs confirm that the deposits are carbonaceous materials. XRD pattern of purified sample indicates that the Fe peaks at 44.6 and 50.9 have been decreased. This confirms that purification process is effectively reducing Fe component. Further qualitative information on the purification process are indicated and confirmed by the thermal analysis measurements. Finally, FTIR studies have been performed for the identification of the functional group attached on the surface of the MWCNTs. Collecting these results revealed that the optimized CVD is suitable for the production of MWCNTs. PMID:24892539

Chemical vapor deposition (CVD) was optimized in order to prepare multi-wallcarbon nanotubes (MWCNTs). Preparation of MWCNTs was achieved by the help of ferrocene as a catalyst with continuous flow of xylene. Morphology and structure of as grown and purified MWCNTs were characterized by Scanning Electron Microscope (SEM) and High-Resolution Transmission Electron Microscope (HRTEM). Energy Dispersive X-ray (EDX) spectra for the as grown MWCNTs confirm that the deposits are carbonaceous materials. XRD pattern of purified sample indicates that the Fe peaks at 44.6 and 50.9 have been decreased. This confirms that purification process is effectively reducing Fe component. Further qualitative information on the purification process are indicated and confirmed by the thermal analysis measurements. Finally, FTIR studies have been performed for the identification of the functional group attached on the surface of the MWCNTs. Collecting these results revealed that the optimized CVD is suitable for the production of MWCNTs.

Research highlights: {yields} Synthesis of carbon nanotubes over Fe-Ni nanoparticles supported alloy 304L. {yields} Production of carbon nanotubes with high yield (700-1000%) and low cost catalyst. {yields} Optimum growth condition is CO/H{sub 2} = 1/1, 100 cm{sup 3}/min, at 620 {sup o}C under long term repetitive thermal cycling. {yields} Possibility of the mass production by metal dusting process with low cost. -- Abstract: Carbon nanotube materials were synthesized over Fe-Ni nanoparticles generated during disintegration of the surface of alloy 304L under metal dusting environment. The metal dusting condition was simulated and optimized through exposing stainless steel samples during long term repetitive thermal cycling in CO/H{sub 2} = 1/1, total gas flow rate 100 cm{sup 3}/min, at 620 {sup o}C for 300 h. After reaction, surface morphology of the samples and also carbonaceous deposition which had grown on sample surfaces were examined by stereoscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Results revealed that multi-wallcarbon nanotubes could be formed over nanocatalyst generated on the alloy surface by exploiting metal dusting process. By optimization of reaction parameters the yields of carbon nanotube materials obtained were 700-1000%. Also it has been shown herein that the amount of carbon nanotube materials remarkably increases when the reaction time is extended up to 300 h, indicating a possibility of the mass production by this easy method.

This research was carried out to evaluate the capability of multi-walledcarbon nanotubes (CNTs) and NiFe2O4-decorated multi-walledcarbon nanotubes (NiFe2O4-CNTs) toward waste water treatment relevant to organic dyes. CNTs were prepared via chemical vapor deposition method. NiFe2O4-CNTs were prepared by in-situ chemical precipitation of metal hydroxides followed by hydrothermal processing. The samples were characterized using XRD and TEM. The adsorption efficiency of CNTs and NiFe2O4-CNTs of methyl green dye at various temperatures was examined. The adsorbed amount increased with the CNTs and NiFe2O4-CNTs dosage. The linear correlation coefficients and standard deviations of Langmuir and Freundlich isotherms were determined. It was found that Langmuir isotherm fitted the experimental results well in both adsorption cases n of methyl green onto CNTs and NiFe2O4-CNTs. Kinetics analyses were conducted using pseudo first-order, second-order and the intraparticle diffusion models. The results showed that the adsorption kinetics was controlled by a pseudo second-order model for adsorption of methyl green onto CNTs and best controlled by pseudo first-order in case of NiFe2O4-CNTs. Changes in the free energy of adsorption (Δ G°), enthalpy (Δ H°), entropy (Δ S°), and the activation energy ( E a) were determined. The Δ H°, Δ G° and E a values indicated that the adsorption of methyl green onto MWCNTs and NiFe2O4-MWCNTs was physisorption.

Carbon nanotubes (CNTs) are being investigated for a variety of biomedical applications. Despite numerous studies, the pathways by which carbon nanotubes enter cells and their subsequent intracellular trafficking and distribution remain poorly determined. Here, we use 3-D electron tomography techniques that offer optimum enhancement of contrast between carbon nanotubes and the plasma membrane to investigate the mechanisms involved in the cellular uptake of shortened, functionalised multi-walledcarbon nanotubes (MWNT-NH3+). Both human lung epithelial (A549) cells, that are almost incapable of phagocytosis and primary macrophages, capable of extremely efficient phagocytosis, were used. We observed that MWNT-NH3+ were internalised in both phagocytic and non-phagocytic cells by any one of three mechanisms: (a) individually via membrane wrapping; (b) individually by direct membrane translocation; and (c) in clusters within vesicular compartments. At early time points following intracellular translocation, we noticed accumulation of nanotube material within various intracellular compartments, while a long-term (14-day) study using primary human macrophages revealed that MWNT-NH3+ were able to escape vesicular (phagosome) entrapment by translocating directly into the cytoplasm.Carbon nanotubes (CNTs) are being investigated for a variety of biomedical applications. Despite numerous studies, the pathways by which carbon nanotubes enter cells and their subsequent intracellular trafficking and distribution remain poorly determined. Here, we use 3-D electron tomography techniques that offer optimum enhancement of contrast between carbon nanotubes and the plasma membrane to investigate the mechanisms involved in the cellular uptake of shortened, functionalised multi-walledcarbon nanotubes (MWNT-NH3+). Both human lung epithelial (A549) cells, that are almost incapable of phagocytosis and primary macrophages, capable of extremely efficient phagocytosis, were used. We observed

Vertically aligned high density small diameter carbon nanotube films were deposited by microwave CVD technique. The iron catalyst was prepared by E-beam evaporation on thermally grown silicon dioxide n-type Si(100) substrates. Experiments show that by continuous reduction in the thickness of Fe (˜ 3-5), smaller diameter carbon nanotube can be achieved. Scanning electron and high-resolution transmission electron microscopy show that the diameter of carbon nanotubes ranged ˜ 1 - 5 nm and the films are comprised of both the single- and double-wall carbon nanotubes. Visible Raman spectroscopy was used to further verify the diameter of nanotubes. A thick iron film (80 nm) was also used to grow nanotubes for comparison. The results show that the catalyst islands become greater than hundred nanometers with increasing thickness and induce multi-wall and bamboo-like microstructures. While for thinner layer of iron films smaller sizes of catalyst particles/droplets produce hollow concentric tubes without bamboo structure and with less number of walls (single-wall and double-wall carbon nanotubes). The base growth was the most appropriate model to describe the growth mechanism for our films. The electron field emission properties such as field electron emission microscopy (FEEM) in conjunction with the temperature dependence (T-FEEM) were measured to investigate the emission site density and their intensity variation. These findings in terms of the role of adsorption will be briefly discussed.

The microbial fuel cell (MFC) is a novel and innovative technology that could allow direct harvesting of energy from wastewater through microbial activity with simultaneous oxidation of organic matter in wastewater. Among all MFC parts, electrode materials play a crucial role in electricity generation. A variety of electrode materials have been used, including plain graphite, carbon paper and carbon cloth. However, these electrode materials generated only limited electricity or power. Recently, many research studies have been conducted on carbon nanotubes (CNTs) because of their unique physical and chemical properties that include high conductivity, high surface area, corrosion resistance, and electrochemical stability. These properties make them extremely attractive for fabricating electrodes and catalyst supports. In this study, CNT-based electrodes had been developed to improve MFC performance in terms of electricity generation and treatment efficiency. Multi-walledcarbon nanotubes (MWCNTs) with carboxyl groups have been employed to fabricate electrodes for single-chamber air-cathode MFCs. The quality of the prepared MWCNTs-based electrodes was evaluated by morphology, electrical conductivity and specific surface area using a field emission scanning electron microscope, four-probe method and Brunauer-Emmerr-Teller method, respectively. The performance of MFCs equipped with MWCNT-based electrodes was evaluated by chemical analysis and electrical monitoring and calculation. In addition, the performance of these MFCs, using MWCNTs as electrodes, was compared against that using commercial carbon cloth. PMID:22437017

alpha-Pyrene functionalised poly(methyl methacrylate) (PMMA) chains were synthesised by RAFT polymerisation and found to be highly efficient to solubilise and disentangle multiwalledcarbon nanotubes that can now self-organise as liquid crystalline phases in PMMA and PEG 400 matrices. PMID:18594730

Multi-walledcarbon nanotube (MWCNT)-based carbon/carbon composites were fabricated by the chemical vapor infiltration of pyrolytic carbon into pre-compressed MWCNT blocks. The pyrolytic carbon was deposited on the surface of the MWCNTs and filled the gaps between the MWCNTs, which improved the connection between the MWCNTs and formed a three-dimensional network structure. The mechanical and electrical properties were improved significantly. The values of the maximum compressed deformation, maximum breaking strength, Young's modulus and energy absorption are measured as 10.9%, 148.6 MPa, 1588.6 MPa and 13.8 kJ kg-1, respectively. The conductivity reached about 204.4 S cm-1, more than 10 times larger than that of pre-compressed MWCNT blocks. After annealing at 1800 °C in vacuum, the graphitization improved remarkably. The pyrolytic carbon deposited on the surface of the MWCNTs was rearranged along the walls, and resulted in an increase of the number of walls of the MWCNTs.Multi-walledcarbon nanotube (MWCNT)-based carbon/carbon composites were fabricated by the chemical vapor infiltration of pyrolytic carbon into pre-compressed MWCNT blocks. The pyrolytic carbon was deposited on the surface of the MWCNTs and filled the gaps between the MWCNTs, which improved the connection between the MWCNTs and formed a three-dimensional network structure. The mechanical and electrical properties were improved significantly. The values of the maximum compressed deformation, maximum breaking strength, Young's modulus and energy absorption are measured as 10.9%, 148.6 MPa, 1588.6 MPa and 13.8 kJ kg-1, respectively. The conductivity reached about 204.4 S cm-1, more than 10 times larger than that of pre-compressed MWCNT blocks. After annealing at 1800 °C in vacuum, the graphitization improved remarkably. The pyrolytic carbon deposited on the surface of the MWCNTs was rearranged along the walls, and resulted in an increase of the number of walls of the MWCNTs. Electronic supplementary

Carbon nanotubes have been the subject of considerable attention because of their exceptional physical and mechanical properties. These properties observed at the nanoscale have motivated researchers to utilize carbon nanotubes as reinforcement in composite materials. In this research, a micro-scale twin-screw extruder was used to achieve dispersion of multi-walledcarbon nanotubes in a polystyrene matrix. Highly aligned nanocomposite films were produced by extruding the polymer melt through a rectangular die and drawing the film prior to cooling. Randomly oriented nanocomposites were produced by achieving dispersion first with the twin-screw extruder followed by pressing a film using a hydraulic press. The tensile behaviour of the aligned and random nanocomposite films with 5 wt.{%} loading of nanotubes were characterized. Addition of nanotubes increased the tensile modulus, yield strength and ultimate strengths of the polymer films, and the improvement in elastic modulus with the aligned nanotube composite is five times greater than the improvement for the randomly oriented composite.

In this study, multi-walledcarbon nanotubes (MWNTs) were employed to remove benzene, toluene, ethylbenzene, and xylenes (BTEX) from low and high salinity water pre-equilibrated with crude oil. The treatment endpoint of crude oil-contaminated water is often controlled by BTEX compounds owing to their higher aqueous solubility and human-health toxicity compared to other hydrocarbons. The MWNT sorbent was extensively characterized and the depletion of the organic sorbate from the produced water was monitored by gas chromatography-mass spectrometry (GC-MS) and total organic carbon (TOC) analyses. The equilibrium sorptive removal of BTEX followed the order: ethylbenzene/o-xylene > m-xylene > toluene > benzene in the presence of other competing organics in produced water. Sorption mechanisms were explored through the application of a variety of kinetics and equilibrium models. Pseudo 2(nd) order kinetics and Freundlich equilibrium models were the best at describing BTEX removal from produced water. Hydrophobic interactions between the MWNTs and BTEX, as well as the physical characteristics of the sorbate molecules, were regarded as primary factors responsible for regulating competitive adsorption. Salinity played a critical role in limiting sorptive removal, with BTEX and total organic carbon (TOC) removal falling by 27% and 25%, respectively, upon the introduction of saline conditions. Results suggest that MWNTs are effective in removing risk-driving BTEX compounds from low-salinity oilfield produced water. PMID:24975808

The impact of carbon nanotubes on the cell membrane is an aspect of particular importance and interest in the study of carbon nanotubes' interactions with living systems. One of the many functions of the cell membrane is to execute substance transport into and out of the cell. We investigated the influence of multi-walledcarbon nanotubes (MWCNTs) on the transport of several compounds across in the cell membrane of rat astrocytes using flow cytometry. These compounds are fluorescein diacetate, carboxyfluorescein diacetate, rhodamine 123 and doxorubicin, which are prosubstrate/substrates of multidrug transporter proteins. Results showed that MWCNTs significantly inhibited cellular uptake of doxorubicin but not the other drugs and the mode of loading made a significant difference in doxorubicin uptake. Retention of fluorescein, carboxyfluorescein and rhodamine 123 was remarkably higher in MWCNT-exposed cells after an efflux period. A kinetics study also demonstrated slower efflux of intracellular fluorescein and rhodamine 123. Data presented in this paper suggest that MWCNTs could affect drug transport across cell membranes. The implications of the findings are discussed.

We study the effects of Ar+, He+ and C+ ion irradiation on multi-walledcarbon nanotubes at room and elevated temperatures with transmission electron microscopy (TEM) and Raman spectroscopy. Based on the TEM data, we introduce a universal damage scale for the visual analysis and characterization of irradiated nanotubes. We show for the first time that the amount of irradiation-induced damage in nanotubes is larger than the value predicted for bulk materials using the simple binary collision approximation, which may be associated with higher defect production due to electronic stopping in these nanoscale systems. The Raman spectra of the irradiated samples are in qualitative agreement with the TEM data and indicate the presence of irradiation-induced defects. However, it is difficult to obtain quantitative information on defect concentration due to non-uniform distribution of defects in the nanotube films and in part due to the presence of other carbon nanosystems in the samples, such as graphitic crystallites and carbon onions.

Multi-walledcarbon nanotubes were synthesized using a Fe-Ni bimetallic catalyst supported by MgO using thermal chemical vapor deposition. Purification processes to remove unwanted carbon structures and other metallic impurities were carried out by boiling in sulfuric acid solution. Various analytical techniques such as TGA/DSC, Raman spectroscopy, SEM, HRTEM and EDAX were employed to investigate the morphology, graphitization and quality of the carbon nanotubes. The obtained results reveal the molarity of sulfuric acid and immersed time of the carbon nanotubes in the acid solution is very effective at purifying multi-walledcarbon nanotubes. It was also found that 5 M concentration of boiling sulfuric acid for a 3 h treatment duration led to the highest removal of the impurities with the least destructive effect. Moreover, it was observed that acid treatment results in decreasing of CNTs' diameter.

Multi-walledcarbon nanotubes were synthesized using a Fe-Ni bimetallic catalyst supported by MgO using thermal chemical vapor deposition. Purification processes to remove unwanted carbon structures and other metallic impurities were carried out by boiling in sulfuric acid solution. Various analytical techniques such as TGA/DSC, Raman spectroscopy, SEM, HRTEM and EDAX were employed to investigate the morphology, graphitization and quality of the carbon nanotubes. The obtained results reveal the molarity of sulfuric acid and immersed time of the carbon nanotubes in the acid solution is very effective at purifying multi-walledcarbon nanotubes. It was also found that 5 M concentration of boiling sulfuric acid for a 3 h treatment duration led to the highest removal of the impurities with the least destructive effect. Moreover, it was observed that acid treatment results in decreasing of CNTs’ diameter.

We used molecular dynamics to investigate the properties of a multi-walledcarbon nanotube based gear. Previous work computationally suggested that molecular gears fashioned from (14,0) single-walled carbon nanotubes operate well at 50-100 gigahertz. The gears were formed from nanotubes with teeth added via a benzyne reaction known to occur with C60. A modified, parallelized version of Brenner's potential was used to model interatomic forces within each molecule. A Leonard-Jones 6-12 potential was used for forces between molecules. The gear in this study was based on the smallest multi-walled nanotube supported by some experimental evidence. Each gear was a (52,0) nanotube surrounding a (37,10) nanotube with approximate 20.4 and 16,8 A radii respectively. These sizes were chosen to be consistent with inter-tube spacing observed by and were slightly larger than graphite inter-layer spacings. The benzyne teeth were attached via 2+4 cycloaddition to exterior of the (52,0) tube. 2+4 bonds were used rather than the 2+2 bonds observed by Hoke since 2+4 bonds are preferred by naphthalene and quantum calculations by Jaffe suggest that 2+4 bonds are preferred on carbon nanotubes of sufficient diameter. One gear was 'powered' by forcing the atoms near the end of the outside buckytube to rotate to simulate a motor. A second gear was allowed to rotate by keeping the atoms near the end of its outside buckytube on a cylinder. The ends of both gears were constrained to stay in an approximately constant position relative to each other, simulating a casing, to insure that the gear teeth meshed. The stiff meshing aromatic gear teeth transferred angular momentum from the powered gear to the driven gear. The simulation was performed in a vacuum and with a software thermostat. Preliminary results suggest that the powered gear had trouble turning the driven gear without slip. The larger radius and greater mass of these gears relative to the (14,0) gears previously studied requires a

The present work describes the development of novel ZnO dispersed multi-walledcarbon nanotubes (MWNT) based non-enzymatic glucose biosensor with 1 M NaOH solution as the supporting electrolyte. For a comparison, the same material has been used for the fabrication of enzymatic biosensor and studied its electrochemical activity with phosphate buffer solution as the electrolyte. MWNT have been synthesized by catalytic chemical vapor decomposition (CCVD) and a simple sol-gel method was used for decorating crystalline ZnO nanoparticles on MWNT. Cyclic voltammetry and chronoamperometry were used to study and optimize the electrochemical performance of the resulting enzymatic and non-enzymatic ZnO/MWNT biosensors. The non enzymatic Nafion/ZnO/MWNT/GC electrode shows linearity in the range 700 nM to 31 mM with the detection limit of 500 nM. Similarly enzymatic biosensor fabricated using Nafion/GOD/ZnO/MWNT on glassy carbon electrode (GCE) shows a linearity from 1 microM to 22 mM. This excellent performance of non enzymatic Nafion/ZnO/MWNT/GC is due to high surface area, good electron transfer rate of ZnO/MWNT and the high electrochemical catalytic activity of ZnO in NaOH solution. PMID:21770093

Carbon nanotubes (CNTs) are widely used in industry, but their environmental impacts on soil microbial communities are poorly known. In this paper, we compare the effect of both raw and acid treated or functionalized (fCNTs) multi-walledcarbon nanotubes (MWCNTs) on soil bacterial communities, applying different concentrations of MWCNTs (0 µg/g, 50 µg/g, 500 µg/g and 5000 µg/g) to a soil microcosm system. Soil DNA was extracted at 0, 2 and 8 weeks and the V3 region of the 16S rRNA gene was PCR-amplified and sequenced using paired-end Illumina bar-coded sequencing. The results show that bacterial diversity was not affected by either type of MWCNT. However, overall soil bacterial community composition, as illustrated by NMDS, was affected only by fMWCNT at high concentrations. This effect, detectable at 2 weeks, remained equally strong by 8 weeks. In the case of fMWCNTs, overall changes in relative abundance of the dominant phyla were also found. The stronger effect of fMWCNTs could be explained by their intrinsically acidic nature, as the soil pH was lower at higher concentrations of fMWCNTs. Overall, this study suggests that fMWCNTs may at least temporarily alter microbial community composition on the timescale of at least weeks to months. It appears, by contrast, that raw MWCNTs do not affect soil microbial community composition. PMID:25825905

The nanocomposites of multi-walledcarbon nanotubes (MWNTs) decorated with nickel nanoparticles were conveniently prepared by a chemical reduction of nickel salt in the present of poly(acrylic acid) grafted MWNTs (PAA- g-MWNTs). Due to the strong interaction between Ni 2+ and -COOH, PAA- g-MWNTs became an excellent supporting material for Ni nanoparticles. The morphology and distribution of Ni nanoparticles on the surface of MWNTs were greatly influenced by the reduction temperatures, the experimental results also showed that the distribution of Ni nanoparticles was greatly improved while the MWNTs were modified by poly(acrylic acid) (PAA). The hydrogenation activity and selectivity of MWNTs decorated with Ni nanoparticles (Ni-MWNTs) for α, β-unsaturated aldehyde (citral) were also studied, and the experimental results showed that the citronellal, an important raw material for flavoring and perfumery industries, is the favorable product with a percentage as high as 86.9%, which is 7 times higher than that of catalyst by Ni-supported active carbon (Ni-AC).

Nanocomposites of aligned multi-walledcarbon nanotubes (CNTs) embedded in a polymer matrix yield a unique combination of thermal and electrical properties and mechanical strength. These properties are intimately related to the composite nanostructure and to the growth and processing conditions. The alignment of the tubes, the filling fraction and the contact junction between the nanotubes are key parameters controlling the composite electrical conductivity. For this purpose, a full description of the composite nanostructure is required. Among the non-destructive scanning probe techniques, scanning spreading resistance microscopy is found to be a powerful technique in identifying the carbon nanotubes with true nanometer resolution, thus competing with SEM and TEM imaging. Additionally, the technique provides valuable information about the electrical conduction mechanism within the composite structure. Indeed, by using a controlled contact force and an appropriate model of conduction at the nanoscale, the tip-CNT contact resistance, the CNT intrinsic resistance and the CNT-epoxy-CNT resistance junction are evaluated. This latter is found to be the factor controlling the overall electrical conductivity of the composite. PMID:22995850

This study examined the influence of multi-walledcarbon nanotubes (MWNTs) on the growth of the unicellular protozoan Tetrahymena pyriformis. Contrary to the findings from most other investigations, our experiment indicated that MWNTs stimulated growth of the cells cultured in proteose peptone yeast extract medium (PPY). Atomic force microscopy images and thermogravimetric analysis showed the spontaneous formation of peptone-MWNT conjugates in the medium by noncovalent binding. Uptake of large amounts of the conjugates by Tetrahymena pyriformis was responsible for growth stimulation, evidenced by images with fluorescently labelled peptone. After the PPY medium was replaced by a filtrated pond water medium (FPW), however, inhibition of the growth of cells exposed to MWNTs occurred. Measurements of the level of malondialdehyde and superoxide dismutase activity demonstrated further that MWNTs might be either toxic or nontoxic, depending on the medium used to cultivate Tetrahymena pyriformis. The biological effects of the interaction of MWNTs with some composites in culture media would be helpful for understanding the mechanisms of the toxicity of carbon nanotubes to living systems.

Phenolic antioxidants of wine were electrochemically oxidized on multi-walledcarbon nanotubes modified glassy carbon electrode (MWNT/GCE) in phosphate buffer solution. Three oxidation peaks were observed at 0.39, 0.61 and 0.83V for red dry wine and 0.39, 0.80 and 1.18 V for white dry wine, respectively, using differential pulse voltammetry at pH 4.0. The oxidation potentials for individual phenolic antioxidants confirmed the integral nature of the analytical signals for the wines examined. A one-step chronocoulometric method at 0.83 and 1.18 V for red and white wines, respectively, has been developed for the evaluation of wine antioxidant capacity (AOC). The AOC is expressed in gallic acid equivalents per 1L of wine. The AOC of white wine was significantly less than red wine (386 ± 112 vs. 1224 ± 184, p<0.0001), as might be expected. Positive correlations were observed between gallic acid equivalent AOC of wine and total antioxidant capacity, based on coulometric titration with electrogenerated bromine (r=0.8957 at n=5 and r=0.8986 at n=4 for red and white wines, respectively). PMID:26593508

The evaporation and condensation of water on multi-walledcarbon nanotube (MWCNT) surfaces was studied as a function of temperature and time using X-ray spatial frequency heterodyne imaging (SFHI). SFHI is an imaging modality that produces an absorption and scatter image in a single exposure, and has increased sensitivity to variations in electron density relative to more common place X-ray imaging techniques. Differing features exhibited in the temporal scatter intensity profiles recorded during evaporation and condensation revealed the existence of an absorption-desorption hysteresis. Effects on the aforementioned phenomena due to chemical functionalization of the carbon nanotube surfaces were also monitored. The increased interaction potential between the functionalized MWCNT walls and water molecules altered the evaporation event time scale and increased the temperature at which condensation could take place. Theoretical calculations were used to correlate the shape of the observed scatter profiles during condensation to changes in the MWCNT cross section geometry and configuration of the contained water volume. Changes in evaporation time scales with temperature coincided with the boiling point for confined water predicted by the Kelvin equation, indicating that a thermodynamic description of mesoscopic confined water is permissible in some instances. PMID:26549826

Multiwalledcarbon nanotubes [MWCNT's] have won enormous popularity in nanotechnology. Due to their unusual one dimensional, hollow nanostructure and unique physicochemical properties they are highly desirable for use within the commercial, environmental and medical sectors. Despite their wide application, there is a lack of information concerning their impact on human health and the environment. While nanotechnology looms large with commercial promise and potential benefit, an equally large issue is the evaluation of potential effects on humans and other biological systems. Our research is focused on cellular response to purified MWCNT in normal human dermal fibroblast cells (NHDF). Three doses (40, 200, 400 μg/ml) of MWCNT and control (tween-80 + 0.9% saline) were used in this study. Following exposure to MWCNT, cytotoxicity, genotoxicity and apoptosis assays were performed using standard protocols. Our results demonstrated a dose-dependent toxicity with MWCNT. It was found to be toxic and induced massive loss of cell viability through DNA damage and programmed cell-death of all doses compared to control. Our results demonstrate that carbon nanotubes indeed can be very toxic at sufficiently high concentrations and that careful monitoring of toxicity studies is essential for risk assessment. PMID:20521388

Carbon nanotubes (CNTs) are of great interest due to their potential applications in different fields such as water treatment and desalination. The increasing exploitation of multi-walledcarbon nanotubes (MWCNTs) into many industrial processes has raised considerable concerns for environmental applications. The interactions of soluble salt with MWNCTs influence in the total salt content in saline water. In this work, we synthesized two cation exchange resins nano composites from polystyrene divinylbenzene copolymer (PSDVB) and pristine MWNCTs. The prepared compounds were characterized using infra red spectroscopy, thermal stability, X-ray diffraction, and electro scan microscope. Also, the ion capacities of prepared cation exchange resins were determined by titration. Based on the experimental results, it was found that the thermal stability of prepared nanocomposites in the presence of MWNCTs increased up to 617 °C. The X-ray of PSDVB and its sulfonated form exhibits amorphous pattern texture structure, whereas the nano composite exhibits amorphous structure with indication peak at 20° and 26° for the PSDVB and MWCNTs, respectively. The ion-exchange capacity increased from 225.6 meq/100 g to 466 mg/100 g for sulfonated PSDVB and sulfonated PSDVB MWNCTs-pristine, respectively.

In this work, polyacrylamide/multi-walledcarbon nanotubes (MWCNT) solution is electrospun to nanocomposite nanofibrous membranes for acetylcholinesterase enzyme immobilization. A new method for enzyme immobilization is proposed, and the results of analysis show successful covalent bonding of enzymes on electrospun membrane surface besides their non-covalent entrapment. Fourier transform infrared spectroscopy, mechanical and thermal investigations of nanofibrous membrane approve successful cross-linking and enzyme immobilization. The enzyme relative activity and kinetic on both pure and nanocomposite membranes is investigated, and the results show proper performance of designed membrane to even improve the enzyme activity followed by immobilization compared to free enzyme. Scanning electron microscopy images show nanofibrous web of 3D structure with a low shrinkage and hydrogel structure followed by enzyme immobilization and cross-linking. Moreover, the important role of functionalized carbon nanotubes on final nanofibrous membrane functionality as a media for enzyme immobilization is investigated. The results show that MWCNT could act effectively for enzyme immobilization improvement via both physical (enhanced fibers' morphology and conductivity) and chemical (enzyme entrapment) methods. PMID:23475318

Composites of linear-low density polyethylene (LLDPE) with multi-walledcarbon nanotubes (MWCNT) and thermally reduced graphene (TRGO) were produced by melt compounding. The composites were compatibilized by grafting aromatic pyridine groups onto the LLDPE backbone. The aromatic moieties established non-covalent π-π interactions with the carbon nanostructures, thus allowing for efficient dispersion, without compromizing their electrical properties. By using identical matrices, it was possible to investigate the effects of filler geometry on the electrical, mechanical and rheological properties of the composites. The 1-D nature and smaller surface area of the MWCNT facilitated their dispersion within the polymer matrix, whereas the graphene agglomerates appeared to breakup through an erosion mechanism. The resulting mixture of aggregates and individual graphene platelets favored lower electrical and rheological percolation thresholds. However the maximum electrical conductivity achieved in the TRGO/LLDPE was lower by about an order of magnitude compared to the MWCNT/LLDPE composites, probably due to residual oxygen in the graphene's structure. TRGO based composites presented higher moduli at the same filler loadings, while elongations at break were comparable. All composites exhibited time-dependent rheological properties, indicative of their tendency to aggregate. A more pronounced increase in viscoelastic properties was noted in the composites containing TRGO, presumably due to the higher surface area of the graphene platelets, and the presence of larger aggregates.

Recent time-resolved measurements of carbon nanotube (CNT) growth on Fe and Fe/Mo catalysts have identified a maximum growth rate and temperature corresponding to the onset of small-diameter, single-wall CNT (SWNT) formation. A simple model described here emphasizes the essential role of the SWNTs in the growth process of CNTs. Remarkably, it shows that the growth rate (i.e. the time derivative of the length) of a multi-walled CNT (MWNT) is the same as that of a SWNT at the carbon flux and diffusion coefficient corresponding to a given temperature. Moreover, below ~700C, the temperature above which SWNT growth is observed for a 6 sccm C2H2 flow rate, the number of walls as a function of temperature is uniquely determined by the interplay of the incident flux of atomic C and diffusion rates consistent with bulk diffusion. Even partial melting of the catalytic particle is unnecessary to explain the experimental results on growth rate and number of walls. Above 700C, where severe catalyst poisoning ordinarily begins, the growth rate without poisoning is consistent with recent results of Hata and co-workers for "supergrowth".

Contrary to the observed positive giant magnetoresistance (GMR) in as-received multi-walledcarbon nanotubes (MWNTs), pure polyaniline (PANI) synthesized with Cr(vi) as oxidant and MWNTs/PANI nanocomposites with ammonium persulfate (APS) as oxidant, a room temperature negative GMR of around -2% was reported in MWNTs/PANI nanocomposites with Cr(vi) as oxidant. Different from a frequency switch of permittivity from negative to positive in MWNTs/PANI nanocomposites with APS as oxidant, unique negative permittivity was observed in MWNTs/PANI nanocomposites with Cr(vi) as oxidant within the measured frequency range from 20 to 2 × 106 Hz. The obtained unique negative permittivity was explained by the plasma frequency from the Drude model, at which the permittivity changes from negative to positive and the material changes from a metamaterial to an ordinary dielectric medium. The observed positive and negative GMR behaviors in these disordered systems as verified by the temperature dependent resistivity exploration were well explained through a wave-function shrinkage model and orbital magnetoconductivity theory by calculating the changed localization length (a0).Contrary to the observed positive giant magnetoresistance (GMR) in as-received multi-walledcarbon nanotubes (MWNTs), pure polyaniline (PANI) synthesized with Cr(vi) as oxidant and MWNTs/PANI nanocomposites with ammonium persulfate (APS) as oxidant, a room temperature negative GMR of around -2% was reported in MWNTs/PANI nanocomposites with Cr(vi) as oxidant. Different from a frequency switch of permittivity from negative to positive in MWNTs/PANI nanocomposites with APS as oxidant, unique negative permittivity was observed in MWNTs/PANI nanocomposites with Cr(vi) as oxidant within the measured frequency range from 20 to 2 × 106 Hz. The obtained unique negative permittivity was explained by the plasma frequency from the Drude model, at which the permittivity changes from negative to positive and the material

The multiphase approach was adapted to enhance the electromagnetic interference (EMI) shielding effectiveness (SE) of polyaniline (PANI) based nanocomposites. The natural graphite flakes (NGF) incorporated modified PANI was used for the development of multi-walledcarbon nanotubes (MWCNTs) based nanocomposites. In PANINGF-MWCNTs composites, multilayer graphene was synthesized in situ by ball milling. The resultant PANINGF-MWCNTs nanocomposites were characterized by different techniques. It was revealed from the transmission electron microscope (TEM) observation that in situ derived multilayer graphene acts as a bridge between PANI and MWCNTs, and plays a significant role for improving the properties of multiphase nanocomposites. It was observed that EMI-SE increases with increasing the MWCNTs content from 1 to 10 wt% in the multiphase nanocomposites. The maximum value of total EMI-SE was -98 dB of nanocomposite with 10 wt% of MWCNTs content. The high value of EMI-SE is dominated by the absorption phenomenon which is due to the collective effect of increase in space charge polarization and decrease in carrier mobility. The decrease in carrier mobility has a positive effect on the shore hardness value due to the strong interaction between the reinforcing constituent in multiphase nanocomposites. As a consequence, shore hardness increases from 56 to 91 at 10 wt% of MWCNTs.The multiphase approach was adapted to enhance the electromagnetic interference (EMI) shielding effectiveness (SE) of polyaniline (PANI) based nanocomposites. The natural graphite flakes (NGF) incorporated modified PANI was used for the development of multi-walledcarbon nanotubes (MWCNTs) based nanocomposites. In PANINGF-MWCNTs composites, multilayer graphene was synthesized in situ by ball milling. The resultant PANINGF-MWCNTs nanocomposites were characterized by different techniques. It was revealed from the transmission electron microscope (TEM) observation that in situ derived multilayer

A nonenzymatic electrochemical sensor device was fabricated for glucose detection based on nickel nanoparticles (NiNPs)/straight multi-walledcarbon nanotubes (SMWNTs) nanohybrids, which were synthesized through in situ precipitation procedure. SMWNTs can be easily dispersed in solution after mild sonication pretreatment, which facilitates the precursor of NiNPs binding to their surface and results in the homogeneous distribution of NiNPs on the surface of SMWNTs. The morphology and component of the nanohybrids were characterized by scanning electron microscopy (SEM) and X-ray powder diffraction (XRD), respectively. Cyclic voltammetry (CV) and amperometry were used to evaluate the catalytic activity of the NiNPs/SMWNTs nanohybrids modified electrode towards glucose. It was found that the nanohybrids modified electrode showed remarkably enhanced electrocatalytic activity towards the oxidation of glucose in alkaline solution compared to that of the bare glass carbon electrode (GCE), the NiNPs and the SMWNTs modified electrode, attributing to the synergistic effect of SMWNTs and Ni(2+)/Ni(3+) redox couple. Under the optimal detection conditions, the as-prepared sensors exhibited linear behavior in the concentration range from 1 μM to 1 mM for the quantification of glucose with a limit of detection of 500 nM (3σ). Moreover, the NiNPs/SMWNTs modified electrode was also relatively insensitive to commonly interfering species such as ascorbic acid (AA), uric acid (UA), dopamine (DA), galactose (GA), and xylose (XY). The robust selectivities, sensitivities, and stabilities determined experimentally indicated the great potential of NiNPs/SMWNTs nanohybrids for construction of a variety of electrochemical sensors. PMID:21955756

This study focused on the development of a sensitive enzymatic biosensor for the determination of pirimicarb pesticide based on the immobilization of laccase on composite carbon paste electrodes. Multi-walledcarbon nanotubes (MWCNTs) paste electrode modified by dispersion of laccase (3%, w/w) within the optimum composite matrix (60:40%, w/w, MWCNTs and paraffin binder) showed the best performance, with excellent electron transfer kinetic and catalytic effects related to the redox process of the substrate 4-aminophenol. No metal or anti-interference membrane was added. Based on the inhibition of laccase activity, pirimicarb can be determined in the range 9.90 × 10(-7) to 1.15 × 10(-5) mol L(-1) using 4-aminophenol as substrate at the optimum pH of 5.0, with acceptable repeatability and reproducibility (relative standard deviations lower than 5%). The limit of detection obtained was 1.8 × 10(-7) mol L(-1) (0.04 mg kg(-1) on a fresh weight vegetable basis). The high activity and catalytic properties of the laccase-based biosensor are retained during ca. one month. The optimized electroanalytical protocol coupled to the QuEChERS methodology were applied to tomato and lettuce samples spiked at three levels; recoveries ranging from 91.0 ± 0.1% to 101.0 ± 0.3% were attained. No significant effects in the pirimicarb electroanalysis were observed by the presence of pro-vitamin A, vitamins B1 and C, and glucose in the vegetable extracts. The proposed biosensor-based pesticide residue methodology fulfills all requisites to be used in implementation of food safety programs. PMID:23598106

Background Carbon nanotubes, graphene, graphite nanoplatelets and carbon black are seemingly chemically identical carbon-based nano-materials with broad technological applications. Carbon nanotubes and carbon black possess different inhalation toxicities, whereas little is known about graphene and graphite nanoplatelets. Methods In order to compare the inhalation toxicity of the mentioned carbon-based nanomaterials, male Wistar rats were exposed head-nose to atmospheres of the respective materials for 6 hours per day on 5 consecutive days. Target concentrations were 0.1, 0.5, or 2.5 mg/m3 for multi-wallcarbon nanotubes and 0.5, 2.5, or 10 mg/m3 for graphene, graphite nanoplatelets and low-surface carbon black. Toxicity was determined after end of exposure and after three-week recovery using broncho-alveolar lavage fluid and microscopic examinations of the entire respiratory tract. Results No adverse effects were observed after inhalation exposure to 10 mg/m3 graphite nanoplatelets or relatively low specific surface area carbon black. Increases of lavage markers indicative for inflammatory processes started at exposure concentration of 0.5 mg/m3 for multi-wallcarbon nanotubes and 10 mg/m3 for graphene. Consistent with the changes in lavage fluid, microgranulomas were observed at 2.5 mg/m3 multi-wallcarbon nanotubes and 10 mg/m3 graphene. In order to evaluate volumetric loading of the lung as the key parameter driving the toxicity, deposited particle volume was calculated, taking into account different methods to determine the agglomerate density. However, the calculated volumetric load did not correlate to the toxicity, nor did the particle surface burden of the lung. Conclusions The inhalation toxicity of the investigated carbon-based materials is likely to be a complex interaction of several parameters. Until the properties which govern the toxicity are identified, testing by short-term inhalation is the best option to identify hazardous properties in

The work focused on manufacturing improved drug loaded multifunctional magnetic nanoparticles that can overcome the relative non-specificity and potential side-effects of some chemotherapeutic drugs to healthy tissues. A new drug delivery system, Chelerythrine (CHE) and Fe3O4 loaded multi-walledcarbon nanotubes (Fe3O4/MWNTs-CHE nanocomposites) that can target hepatocytes when treating malignant tumors, was prepared through a simple adsorption method. The formulation and structure of the Fe3O4/MWNTs-CHE nanocomposites were characterized by vibrating sample magnetometer (VSM), Fourier Transform infrared spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). The cytotoxicity and anti-proliferation effect from the prepared nanocomposites were in vitro tested on human hepatocarcinoma HepG2 and normal liver LO2 cell lines. The results showed the saturated magnetization of Fe3O4/MWNTs-CHE nanocomposites could reach to 45.4O3 emu/g, and the in vitro CHE release behavior exhibited a biphasic release pattern. Moreover, the in vitro cytotoxicity studies revealed that the Fe3O4/MWNTs-CHE nanocomposites showed an efficient inhibition rate to HepG2 cell line and exhibited a lower cytotoxicity to LO2 cell line in comparison to the native CHE. Therefore, the multifunctional Fe3O4/MWNTs-CHE nanocomposites should be a useful and promising candidate for treatment of malignant tumors. PMID:27319224

Many studies have used a carbon nanotube (CNT) filter for pathogen removal and/or inactivation by means of electrochemical or electrochlorination. The large surface area, fine pore size and high electrical and thermal conductivity of CNTs make them suitable and distinct to use for the filtering and removal of pathogens. Here, we grew spin-capable multi-walled CNTs (MWCNTs) and manufactured a web filter using the spun MWCNTs. Botulinum toxin type E light chain (BoT/E-LC) and vaccinia virus (VV) were filtered using the MWCNT web filters and were evaporated and removed by applying direct current (DC) voltage to both sides of the MWCNT webs, excluding electrochemical or electrochlorination. The filtering and removal of BoT/E-LC and VV were performed after seven layers of the MWCNT sheets were coated onto a silicon oxide porous plate. The electrical resistance of the webs in the seven layer sheet was 293 Ω. The temperature of MWCNTs webs was linearly increased to ˜300 °C at 210 V of DC voltage. This temperature was enough to remove BoT/E-LC and VV. From the SEM and XPS results, we confirmed that BoT/E-LC and VV on the MWCNT webs were almost removed by applying a DC voltage and that some element (N, Na, Cl, etc.) as residues on the MWCNT webs remained.

We report the direct electrochemical and electrocatalytic properties of myoglobin (MB) on a multi-walledcarbon nanotube/ciprofloxacin (MWCNT/CF) film-modified electrode. A highly homogeneous MWCNT thin-film was prepared on an electrode surface using ciprofloxacin (CF) as a dispersing agent. MB was then electrochemically deposited onto the MWCNT/CF-modified electrode. The MB/MWCNT/CF film was characterized by scanning electron microscopy and UV-visible spectroscopy (UV-vis). UV-vis spectra confirmed that MB retained its original state on the MWCNT/CF film. Direct electrochemical properties of MB on the MWCNT/CF film were investigated by cyclic voltammetry. The formal potential and electron transfer rate constant were evaluated in pH 7.2 buffer solution as -0.327V and 300s(-1), respectively. In addition, the MB/MWCNT/CF-modified electrode showed excellent electrocatalytic properties for the reduction of hydrogen peroxide (H(2)O(2)). The MB/MWCNT/CF-modified electrode was used for the detection of H(2)O(2) at concentrations from 1×10(-6)M to 7×10(-4)M in pH 7.2 buffer solution. Overall, the MB/MWCNT/CF-modified electrode was very stable and has potential for development as a H(2)O(2) sensor. PMID:21115278

This work addresses the comparison of different strategies for improving biosensor performance using nanomaterials. Glucose biosensors based on commonly applied enzyme immobilization approaches, including sol-gel encapsulation approaches and glutaraldehyde cross-linking strategies, were studied in the presence and absence of multi-walledcarbon nanotubes (MWNTs). Although direct comparison of design parameters such as linear range and sensitivity is intuitive, this comparison alone is not an accurate indicator of biosensor efficacy, due to the wide range of electrodes and nanomaterials available for use in current biosensor designs. We proposed a comparative protocol which considers both the active area available for transduction following nanomaterial deposition and the sensitivity. Based on the protocol, when no nanomaterials were involved, TEOS/GOx biosensors exhibited the highest efficacy, followed by BSA/GA/GOx and TMOS/GOx biosensors. A novel biosensor containing carboxylated MWNTs modified with glucose oxidase and an overlying TMOS layer demonstrated optimum efficacy in terms of enhanced current density (18.3 ± 0.5 µA mM - 1 cm - 2), linear range (0.0037-12 mM), detection limit (3.7 µM), coefficient of variation (2%), response time (less than 8 s), and stability/selectivity/reproducibility. H2O2 response tests demonstrated that the most possible reason for the performance enhancement was an increased enzyme loading. This design is an excellent platform for versatile biosensing applications.

The valine functionalized multi-walledcarbon nanotubes (MWCNTS) were prepared and characterized by using XRD, UV-Vis, FT-IR, EPR, SEM, and EDX, spectroscopic techniques. The enhanced XRD peak (0 0 2) intensity was observed for valine functionalized MWCNTs compared with oxidized MWCNTs, which is likely due to sample purification by acid washing. UV-Vis study shows the formation of valine functionalized MWCNTs. FT-IR study confirms the presence of functional groups of oxidized MWCNTs and valine functionalized MWCNTs. The ESR line shape analysis indicates that the observed EPR line shape is a Gaussian line shape. The g-values indicate that the systems are isotropic in nature. The morphology study was carried out for oxidized MWCNTs and valine functionalized MWCNTs by using SEM. The EDX spectra revealed that the high purity of oxidized MWCNTs and valine functionalized MWCNTs. The functionalization has been chosen because, functionalization of CNTs with amino acids makes them soluble and biocompatible. Thus, they have potential applications in the field of biosensors and targeted drug delivery.

A zirconia/multi-walledcarbon nanotube (ZrO2/MWCNT) mesoporous composite was fabricated via a simple method using a hydrothermal process with the aid of the cationic surfactant cetyltrimethylammonium bromide (CTAB). Transmission electron microscopy (TEM), N2 adsorption-desorption, Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) techniques were used to characterize the as-made samples. The cubic ZrO2 nanocrystallites were observed to overlay the surface of MWCNTs, which resulted in the formation of a novel mesoporous-nanotube composite. On the basis of a TEM analysis of the products from controlled experiment, the role of the acid-treated MWCNTs and CTAB was proposed to explain the formation of the mesoporous-nanotube structure. The as-made composite possessed novel properties, such as a high surface area (312 m(2)·g(-1)) and a bimodal mesoporous structure (3.18 nm and 12.4 nm). It was concluded that this composite has important application value due to its one-dimensional hollow structure, excellent electric conductivity and large surface area. PMID:23910298

In this work we have fabricated hydrogen gas sensors based on undoped and 1 wt% multi-walledcarbon nanotube (MWCNT)-doped tungsten oxide (WO3) thin films by means of the powder mixing and electron beam (E-beam) evaporation technique. Hydrogen sensing properties of the thin films have been investigated at different operating temperatures and gas concentrations ranging from 100 ppm to 50,000 ppm. The results indicate that the MWCNT-doped WO3 thin film exhibits high sensitivity and selectivity to hydrogen. Thus, MWCNT doping based on E-beam co-evaporation was shown to be an effective means of preparing hydrogen gas sensors with enhanced sensing and reduced operating temperatures. Creation of nanochannels and formation of p-n heterojunctions were proposed as the sensing mechanism underlying the enhanced hydrogen sensitivity of this hybridized gas sensor. To our best knowledge, this is the first report on a MWCNT-doped WO3 hydrogen sensor prepared by the E-beam method. PMID:22163623

We report on the growth and fabrication of Ni-filled multi-walledcarbon nanotubes (Ni-MWNTs) with an average diameter of 115 nm and variable length of 400 nm-1 µm. The Ni-MWNTs were grown using template-assisted electrodeposition and low pressure chemical vapor deposition (LPCVD) techniques. Anodized alumina oxide (AAO) templates were fabricated on Si using a current controlled process. This was followed by the electrodeposition of Ni nanowires (NWs) using galvanostatic pulsed current (PC) electrodeposition. Ni NWs served as the catalyst to grow Ni-MWNTs in an atmosphere of H2/C2H2 at a temperature of 700 °C. Time dependent depositions were carried out to understand the diffusion and growth mechanism of Ni-MWNTs. Characterization was carried out using scanning electron microscopy (SEM), focused ion beam (FIB) milling, transmission electron microscopy (TEM), Raman spectroscopy and energy dispersive x-ray spectroscopy (EDX). TEM analysis revealed that the Ni nanowires possess a fcc structure. To understand the effects of the electrodeposition parameters, and also the effects of the high temperatures encountered during MWNT growth on the magnetic properties of the Ni-MWNTs, vibrating sample magnetometer (VSM) measurements were performed. The template-based fabrication method is repeatable, efficient, enables batch fabrication and provides good control on the dimensions of the Ni-MWNTs. PMID:21606563

The preparation, characterization, and properties of poly(methyl methacrylate) (PMMA)/multi-walledcarbon nanotubes (MWCNTs) nanocomposites are described. Nanocomposites have been prepared by melt-blending in a batch mixer. Both unmodified and surface modified MWCNTs have been used for the nanocomposites preparation. Using both unmodified and modified MWCNTs, the effect of surface modification in nanocomposites is investigated by focusing on three major aspects: dispersion characteristics, mechanical properties, and electrical conductivity measurements. Dispersion of the MWCNTs in the PMMA matrix is examined by scanning and transmission electron microscopy that revealed a homogeneous distribution-dispersion of MWCNTs in the PMMA matrix for both unmodified and modified MWCNTs. Thermomechanical behavior is studied by dynamic mechanical analyzer and results showed a substantial improvement in the mechanical properties of PMMA in conjunction to an increase in the elastic behavior. The tensile properties of neat PMMA moderately improved after nanocomposites preparation with both modified and unmodified MWCNTs, however, electrical conductivity of neat PMMA significantly improved after nanocomposites preparation with 2 wt% unmodified MWCNTs. For example, the through plane conductivity increased from 3.6 x 10(-12) S x cm(-1) for neat PMMA to 3.6 x 10(-9) S x cm(-1) for nanocomposite. The various property measurements have been conducted and results have shown that, in overall, surface modifications have very little or no effect on final properties of neat PMMA. PMID:17663251

This communication describes the preparation, characterization and properties of biodegradable poly(butylene succinate) (PBS)/multi-walledcarbon nanotubes (MWCNTs) nanocomposite. Nanocomposite was prepared by melt-blending in a batch mixer and the amount of MWCNTs loading was 3 wt%. State of dispersion-distribution of the MWCNTs in the PBS matrix was examined by scanning and transmission electron microscopic observations that revealed homogeneous distribution of stacked MWCNTs in PBS matrix. The investigation of the thermomechanical behavior was performed by dynamic mechanical thermal analysis. Results demonstrated substantial enhancement in the mechanical properties of PBS, for example, at room temperature, storage flexural modulus increased from 0.64 GPa for pure PBS to 1.2 GPa for the nanocomposite, an increase of about 88% in the value of the elastic modulus. The tensile modulus and thermal stability of PBS were moderately improved after nanocomposite preparation with 3 wt% of MWCNTs, while electrical conductivity of neat PBS dramatically increased after nanocomposite formation. For example, the in plane conductivity increased from 5.8 x 10(-9) S/cm for neat PBS to 4.4 x 10(-3) for nanocomposite, an increase of 10(6) fold in value of the electrical conductivity. PMID:17025148

A multi-walledcarbon nanotube (MWCNT) - terminated SPM cantilever, was utilized to perform nanolithography and surface diffusion measurements on a thin film of vapor-deposited lithium atop a silicon (111) substrate under ultra-high vacuum conditions. In these investigations the MWCNT tip was shown to act as both a lithium nanopipette and a probe for non-contact atomic force microscopy (NC-AFM) measurements. With the application of appropriate bias conditions, the MWCNT could site-selectively extract (expel) nano-scale amounts of lithium from (to) the sample surface. Depressions, mounds, and spikes were generated on the surface in this way and were azimuthally symmetric about the selected point of pipetting. Following lithium transfer to/from the substrate, the MWCNT pipette-induced features were sequentially imaged with NC-AFM using the MWCNT as the probe. Vacancy pits of ca. 300 nm diameter and 1.5 nm depth were observed to decay on a timescale of hours at room temperature, through diffusion-limited decay processes. A continuum model was utilized to simulate the island decay rates, and the lithium surface diffusion coefficient of D =7.5 (+/-1.3)*10-15 cm2/s was extracted. U.S. Department of Energy Award Number DESC0001160.

In this paper, multi-walledcarbon nanotube (MWCNT) ink was selectively patterned by inkjet printing on substrates to form conductive traces and electrodes for interconnection application. MWCNT was firstly functionalized using concentrated acid and dispersed in deionized water to form a colloidal solution. Various concentrations of MWCNT were formulated to test the stability of the solution. The printability of the MWCNT ink was examined against printing temperature, ink concentration and ink droplet pitch. Rheological properties of the ink were determined by rheometer and sessile drop method. The electrical conductivity of the MWCNT pattern was measured against multiple printing of MWCNT on the same pattern (up to 10 layers). While single layer printing pattern exhibited highest resistance, the CNT entangled together and formed a random network with more printed layers has higher conductivity. The electrical properties of the printed film was compared to a composite ink of CNT and conducting polymer (CNT ink was mixed with conductive polymer solution, Poly(3,4-ethylenedioxythiophene)-Poly(styrenesulfonate) (PEDOT:PSS)). Scanning electron microscopy (SEM) was used to observe the surface structure and atomic force microscopy (AFM) was used to study the morphology of the printed film under different conditions. PMID:21128484

The incorporation of multi-wallcarbon nanotubes at weight fractions of 0.5% wt. and 1% wt. in a PRIMASET cyanate ester system (PT-30) was examined. The thermo-mechanical and electrical properties of the developed nanopolymers were investigated and were compared with the neat matrix properties. A preparation method was developed for the incorporation of the fillers in the resin system. The phenomenon of re-agglomeration of nanotubes took place in the first stages of curing schedule but nevertheless according to the SEM images a good dispersion was generally achieved. DSC, DMA, TGA and thermal conductivity tests were performed for the thermal characterization. For the electrical characterization, AC and DC measurements took place. No significant change in the glass transition temperature (Tg), thermal conductivity and mass loss values was observed in comparison with the neat resin systems. However, in both cases the improvement of electrical conductivity was about nine orders of magnitude, indicating that percolation had been achieved. The elastic modulus in bending was examined and a slight increase was observed in direct comparison with the neat resin. Finally, the developed doped nanopolymer was used as matrix for the CFRPs manufacturing. A full manufacturing protocol was developed in order to overcome the challenging issues concerning the cyanate esters' handling and manufacturing processes. Moreover AC and DC measurements were performed along with thermal conductivity measurements and TMA. The produced modified composites were tested for short beam strength.

We report the first attempt to prepare a flexoelectric nanogenerator consisting of direct-grown piezoelectrics on multi-walledcarbon nanotubes (mwCNT). Direct-grown piezoelectrics on mwCNTs are formed by a stirring and heating method using a Pb(Zr0.52Ti0.48)O3 (PZT)-mwCNT precursor solution. We studied the unit cell mismatch and strain distribution of epitaxial PZT nanoparticles, and found that lattice strain is relaxed along the growth direction. A PZT-mwCNT nanogenerator was found to produce a peak output voltage of 8.6 V and an output current of 47 nA when a force of 20 N is applied. Direct-grown piezoelectric nanogenerators generate a higher voltage and current than simple mixtures of PZT and CNTs resulting from the stronger connection between PZT crystals and mwCNTs and an enhanced flexoelectric effect caused by the strain gradient. These experiments represent a significant step toward the application of nanogenerators using piezoelectric nanocomposite materials.

This work addresses the comparison of different strategies for improving biosensor performance using nanomaterials. Glucose biosensors based on commonly applied enzyme immobilization approaches, including sol-gel encapsulation approaches and glutaraldehyde cross-linking strategies, were studied in the presence and absence of multi-walledcarbon nanotubes (MWNTs). Although direct comparison of design parameters such as linear range and sensitivity is intuitive, this comparison alone is not an accurate indicator of biosensor efficacy, due to the wide range of electrodes and nanomaterials available for use in current biosensor designs. We proposed a comparative protocol which considers both the active area available for transduction following nanomaterial deposition and the sensitivity. Based on the protocol, when no nanomaterials were involved, TEOS/GOx biosensors exhibited the highest efficacy, followed by BSA/GA/GOx and TMOS/GOx biosensors. A novel biosensor containing carboxylated MWNTs modified with glucose oxidase and an overlying TMOS layer demonstrated optimum efficacy in terms of enhanced current density (18.3 ± 0.5 µA mM(-1) cm(-2)), linear range (0.0037-12 mM), detection limit (3.7 µM), coefficient of variation (2%), response time (less than 8 s), and stability/selectivity/reproducibility. H(2)O(2) response tests demonstrated that the most possible reason for the performance enhancement was an increased enzyme loading. This design is an excellent platform for versatile biosensing applications. PMID:21828892

We report the first attempt to prepare a flexoelectric nanogenerator consisting of direct-grown piezoelectrics on multi-walledcarbon nanotubes (mwCNT). Direct-grown piezoelectrics on mwCNTs are formed by a stirring and heating method using a Pb(Zr0.52Ti0.48)O3 (PZT)-mwCNT precursor solution. We studied the unit cell mismatch and strain distribution of epitaxial PZT nanoparticles, and found that lattice strain is relaxed along the growth direction. A PZT-mwCNT nanogenerator was found to produce a peak output voltage of 8.6 V and an output current of 47 nA when a force of 20 N is applied. Direct-grown piezoelectric nanogenerators generate a higher voltage and current than simple mixtures of PZT and CNTs resulting from the stronger connection between PZT crystals and mwCNTs and an enhanced flexoelectric effect caused by the strain gradient. These experiments represent a significant step toward the application of nanogenerators using piezoelectric nanocomposite materials. PMID:27406631

This work aims to study the optimum sintering conditions of hydroxyapatite/functionalized multi-walledcarbon nanotube (HA/f-MWCNT) composite with improved mechanical properties for bone implant applications using a pressureless sintering technique. The carboxyl functional group (COOH) introduced by the acid treatment on the MWCNT surface by which HA molecules are grafted onto the surface of functionalized MWCNT with strong interfacial bonding. The composite exhibits a lower hemolytic rate of 1.27%. The flexible nature of f-MWCNT makes them bend and attached to the HA grains, indicates that f-MWCNT bear significant stress by sharing a portion of the load and it leads to improve their mechanical properties. The maximum Vickers hardness of 3.6GPa is obtained for the HA/f-MWCNT composite sintered at 1100°C, whereas the highest compressive strength of 481.7MPa and fracture toughness of 2.38MPa.m(1/2) achieved after sintering at 1150°C. This study demonstrated that HA/f-MWCNT composite create suitable structures by vacuum pressureless sintering technique to satisfy the mechanical requirements for bone tissues. PMID:27287138

Contrary to the observed positive giant magnetoresistance (GMR) in as-received multi-walledcarbon nanotubes (MWNTs), pure polyaniline (PANI) synthesized with Cr(vi) as oxidant and MWNTs/PANI nanocomposites with ammonium persulfate (APS) as oxidant, a room temperature negative GMR of around -2% was reported in MWNTs/PANI nanocomposites with Cr(vi) as oxidant. Different from a frequency switch of permittivity from negative to positive in MWNTs/PANI nanocomposites with APS as oxidant, unique negative permittivity was observed in MWNTs/PANI nanocomposites with Cr(vi) as oxidant within the measured frequency range from 20 to 2 × 10(6) Hz. The obtained unique negative permittivity was explained by the plasma frequency from the Drude model, at which the permittivity changes from negative to positive and the material changes from a metamaterial to an ordinary dielectric medium. The observed positive and negative GMR behaviors in these disordered systems as verified by the temperature dependent resistivity exploration were well explained through a wave-function shrinkage model and orbital magnetoconductivity theory by calculating the changed localization length (a0). PMID:24226933

To decrease the impedance of microelectrode arrays, for neuroscience applications we have fabricated and tested MEA based on multi-walledcarbon nanotubes. With decreasing physical size of a microelectrode, its impedance increases and charge-transfer capability decreases. To decrease the impedance, the effective surface area of the electrode must generally be increased. We explored the effect of plasma treatment on the surface wettability of MWCNT. With a steam-plasma treatment the surface of MWCNT becomes converted from superhydrophobic to superhydrophilic; this hydrophilic property is attributed to -OH bonding on the surface of MWCNT. We reported the synthesis at 400 °C of MWCNT on nickel-titanium multilayered metal catalysts by thermal chemical vapor deposition. Applying plasma with a power less than 25 W for 10 s improved the electrochemical and biological properties, and circumvented the limitation of the surface reverting to a hydrophobic condition; a hydrophilic state is maintained for at least one month. The MEA was used to record neural signals of a lateral giant cell from an American crayfish. The response amplitude of the action potential was about 275 µV with 1 ms period; the recorded data had a ratio of signal to noise up to 40.12 dB. The improved performance of the electrode makes feasible the separation of neural signals and the recognition of their distinct shapes. With further development the rapid treatment will be useful for long-term recording applications.

The valine functionalized multi-walledcarbon nanotubes (MWCNTS) were prepared and characterized by using XRD, UV-Vis, FT-IR, EPR, SEM, and EDX, spectroscopic techniques. The enhanced XRD peak (002) intensity was observed for valine functionalized MWCNTs compared with oxidized MWCNTs, which is likely due to sample purification by acid washing. UV-Vis study shows the formation of valine functionalized MWCNTs. FT-IR study confirms the presence of functional groups of oxidized MWCNTs and valine functionalized MWCNTs. The ESR line shape analysis indicates that the observed EPR line shape is a Gaussian line shape. The g-values indicate that the systems are isotropic in nature. The morphology study was carried out for oxidized MWCNTs and valine functionalized MWCNTs by using SEM. The EDX spectra revealed that the high purity of oxidized MWCNTs and valine functionalized MWCNTs. The functionalization has been chosen because, functionalization of CNTs with amino acids makes them soluble and biocompatible. Thus, they have potential applications in the field of biosensors and targeted drug delivery. PMID:25554963

Non-covalent functionalization of multi-walledcarbon nanotubes (MWCNTs) by a pyrene based benzo-18-crown-6 ether 1 leads to nanostructure assemblies that play both the role of an ion-to-electron transducer and a selective recognition element in solid-contact ion-selective-electrodes (SC-ISEs). The high loading capacity (36 wt%) as well as the suitable dispersion character of the MWCNT hybrid in the ion-selective membrane (ISM) confirmed the benefit of this approach over the covalent one. The sensor has been applied successfully to the detection of potassium. Nernstian response (56.9 ± 0.9 mV per decade) was obtained (10(-5) and 10(-2) M K(+)) and the selectivity pattern was not altered by the immobilization of the ionophore on the MWCNTs. Leakage of the ionophore from the polymeric matrix is therefore avoided while the sensor construction was simplified and the analytical performances were maintained. PMID:23515323

Oxidized multi-walledcarbon nanotubes (MWCNTs) with different oxygen contents were investigated for the adsorption of tetracycline (TC) from aqueous solutions. As the surface oxygen content of the MWCNTs increased, the maximum adsorption capacity and adsorption coefficient of TC increased to the largest values and then decreased. The relation can be attributed to the interplay between the nanotubes' dispersibility and the water cluster formation upon TC adsorption. The overall adsorption kinetics of TC onto CNTs-3.2%O might be dependent on both intra-particle diffusion and boundary layer diffusion. The maximum adsorption capacity of TC on CNTs-3.2%O was achieved in the pH range of 3.3–8.0 due to formation of water clusters or H-bonds. Furthermore, the presence of Cu2+ could significantly enhanced TC adsorption at pH of 5.0. However, the solution ionic strength did not exhibit remarkable effect on TC adsorption. In addition, when pH is beyond the range (3.3–8.0), the electrostatic interactions caused the decrease of TC adsorption capacity. Our results indicate that surface properties and aqueous solution chemistry play important roles in TC adsorption on MWCNTs. PMID:24937315

In this paper, we propose strain-sensitive thin films based on chemically reduced graphene oxide (GO) and multi-walledcarbon nanotubes (MWCNTs) without adding any further surfactants. In spite of the insulating properties of the thin-film-based GO due to the presence functional groups such as hydroxyl, epoxy, and carbonyl groups in its atomic structure, a significant enhancement of the film conductivity was reached by chemical reduction with hydro-iodic acid. By optimizing the MWCNT content, a significant improvement of electrical and mechanical thin film sensitivity is realized. The optical properties and the morphology of the prepared thin films were studied using ultraviolet-visible spectroscopy (UV-Vis) and scanning electron microscope (SEM). The UV-Vis spectra showed the ability to tune the band gap of the GO by changing the MWCNT content, whereas the SEM indicated that the MWCNTs were well dissolved and coated by the GO. Investigations of the piezoresistive properties of the hybrid nanocomposite material under mechanical load show a linear trend between the electrical resistance and the applied strain. A relatively high gauge factor of 8.5 is reached compared to the commercial metallic strain gauges. The self-assembled hybrid films exhibit outstanding properties in electric conductivity, mechanical strength, and strain sensitivity, which provide a high potential for use in strain-sensing applications.

In this study, the hydrogen storage behaviors of p-type multi-walledcarbon nanotubes (MWNTs) were investigated through the surface modification of MWNTs by immersing them in sulfuric acid (H{sub 2}SO{sub 4}) and hydrogen peroxide (H{sub 2}O{sub 2}) at various ratios. The presence of acceptor-functional groups on the p-type MWNT surfaces was confirmed by X-ray photoelectron spectroscopy. Measurement of the zeta-potential determined the surface charge transfer and dispersion of the p-type MWMTs, and the hydrogen storage capacity was evaluated at 77 K and 1 bar. From the results obtained, it was found that acceptor-functional groups were introduced onto the MWNT surfaces, and the dispersion of MWNTs could be improved depending on the acid-mixed treatment conditions. The hydrogen storage was increased by acid-mixed treatments of up to 0.36 wt% in the p-type MWNTs, compared with 0.18 wt% in the As-received MWNTs. Consequently, the hydrogen storage capacities were greatly influenced by the acceptor-functional groups of p-type MWNT surfaces, resulting in increased electron acceptor–donor interaction at the interfaces. - Graphical abstract: Hydrogen storage behaviors of the p-type MWNTs with the acid-mixed treatments are described. Display Omitted Display Omitted.

A series of cobalt oxide/multi-walledcarbon nanotube (Co 3O 4/MWCNT) composites are successfully synthesized by a facile chemical co-precipitation method followed by a simple thermal treatment process. The morphology and structure of as-obtained composites are characterized by X-ray diffraction, scanning electron microscopy, and N 2-adsorption/desorption measurements, and the electrochemical properties are investigated by cyclic voltammetry (CV), galvanostatic charge/discharge and electrochemical impedance spectroscopy (EIS). For all Co 3O 4/MWCNT composites, MWCNTs are well dispersed in the loosely packed Co 3O 4 nanoparticles. Among them, the Co 3O 4-5%MWCNT composite exhibits the highest specific surface area of 137 m 2 g -1 and a mesoporous structure with a narrow distribution of pore size from 2 to 10 nm. Because of the synergistic effects coming from Co 3O 4 nanoparticles and MWCNTs, the electrochemical performances of pure Co 3O 4 material are significantly improved after adding MWCNTs. The Co 3O 4-5%MWCNT composite shows the largest specific capacitance of 418 F g -1 at a current density of 0.625 A g -1 in 2 M KOH electrolyte. Furthermore, this composite exhibits good cycling stability and lifetime. Therefore, based on the above investigation, such Co 3O 4/MWCNT composite could be a potential candidate for supercapacitors.

Alginate is a hydrogel commonly used for cell culture by ionically crosslinking in the presence of divalent Ca2+ ions. However these alginate gels are mechanically unstable, not permitting their use as scaffolds to engineer robust biological bone, breast, cardiac or tumor tissues. This issue can be addressed via encapsulation of multi-walledcarbon nanotubes (MWCNT) serving as a reinforcing phase while being dispersed in a continuous phase of alginate. We hypothesized that adding functionalized MWCNT to alginate, would yield composite gels with distinctively different mechanical, physical and biological characteristics in comparison to alginate alone. Resultant MWCNT-alginate gels were porous, and showed significantly less degradation after 14 days compared to alginate alone. In vitro cell-studies showed enhanced HeLa cell adhesion and proliferation on the MWCNT-alginate compared to alginate. The extent of cell proliferation was greater when cultured atop 1 and 3 mg/ml MWCNT-alginate; although all MWCNT-alginates lead to enhanced cell cluster formation compared to alginate alone. Among all the MWCNT-alginates, the 1 mg/ml gels showed significantly greater stiffness compared to all other cases. These results provide an important basis for the development of the MWCNT-alginates as novel substrates for cell culture applications, cell therapy and tissue engineering. PMID:27578567

Oxidized multi-walledcarbon nanotubes (MWCNTs) with different oxygen contents were investigated for the adsorption of tetracycline (TC) from aqueous solutions. As the surface oxygen content of the MWCNTs increased, the maximum adsorption capacity and adsorption coefficient of TC increased to the largest values and then decreased. The relation can be attributed to the interplay between the nanotubes' dispersibility and the water cluster formation upon TC adsorption. The overall adsorption kinetics of TC onto CNTs-3.2%O might be dependent on both intra-particle diffusion and boundary layer diffusion. The maximum adsorption capacity of TC on CNTs-3.2%O was achieved in the pH range of 3.3-8.0 due to formation of water clusters or H-bonds. Furthermore, the presence of Cu2+ could significantly enhanced TC adsorption at pH of 5.0. However, the solution ionic strength did not exhibit remarkable effect on TC adsorption. In addition, when pH is beyond the range (3.3-8.0), the electrostatic interactions caused the decrease of TC adsorption capacity. Our results indicate that surface properties and aqueous solution chemistry play important roles in TC adsorption on MWCNTs.

The interaction of multi-walledcarbon nanotubes (MWCNTs) with catalase is investigated using fluorescence and circular dichroism spectroscopic techniques. The results of the fluorescence experiments suggest that MWCNTs quench the intrinsic fluorescence of catalase via a static quenching mechanism. The circular dichroism spectral results reveal the unfolding of catalase with a significant decrease in the α-helix content in the presence of MWCNTs, which indicates that the conformation of catalase is changed in the binding process, thereby remarkably decreasing its activity. The binding constants and the number of binding sites of the MWCNT to the catalase are calculated at different temperatures. The thermodynamic parameters, such as the changes in free energy (ΔG), enthalpy (ΔH), and entropy (ΔS), are calculated using thermodynamic equations. The fact that all negative values of ΔG, ΔH, and ΔS are obtained suggests that the interaction of the MWCNTs with catalase is spontaneous, and that hydrogen bonding and van der Waals interactions play an important role in the binding process.

Nanotechnology is one of the most important technologies in this century and it is evoking a new industrial revolution. Carbon nanotubes (CNTs) are important engineered nanoparticles with unique and beneficial properties. As a result, CNT has been used in a wide range of commercial products including electronics, optical devices and drug delivery leading to their disposal in the natural environment. Literature studies have investigated the mobility of CNTs in saturated porous media under differing physical and chemical conditions. However CNT transport in temporarily changing porous media water content has not been investigated thus far (a common scenario with rainfall/infiltration events in the vadose zone). This study investigated the mobilization of multi-walled CNTs (MCNTs) in repeated wetting and drying cycles with varying flow rates and ionic strength of the inflow solution. Imbibition-drainage-imbibition cycle experiments suggest that MCNTs mobilization increased with increase in flow rates. MCNTs mobilization occurred only with first imbibition events at low ionic strengths however less mobilization happened for higher ionic strength inflow solution in the first imbibition cycle and additional MCNTs were found in the outflow solution in second imbibition cycle, using low ionic strength solution. This observation was likely due to the attachment force between MCNTs and sand surface. Most of the MCNT mobilization occurred during liquid-gas interface movement with less chance of MCNTs to jump the energy barrier at higher ionic strength solution. As a result, less detachment of MCNTs occurred from the sand surface during drainage.

Strengthening behavior of the aluminum composites reinforced with chopped multi-walledcarbon nanotubes (MWCNTs) or aluminum carbide formed during annealing at 500 °C has been investigated. The composites were fabricated by hot-rolling the powders which were ball-milled under various conditions. During the early annealing process, aluminum atoms can cluster inside the tube due to the diffusional flow of aluminum atoms into the tube, providing an increase of the strength of the composite. Further annealing induces the formation of the aluminum carbide phase, leading to an overall drop in the strength of the composites. While the strength of the composites can be evaluated according to the rule of mixture, a particle spacing effect can be additionally imparted on the strength of the composites reinforced with the chopped MWCNTs or the corresponding carbides since the reinforcing agents are smaller than the submicron matrix grains. - Highlights: • Strengthening behavior of chopped CNT reinforced Al-based composites is investigated. • Chopped CNTs have influenced the strength and microstructures of the composites. • Chopped CNTs are created under Ar- 3% H2 atmosphere during mechanical milling. • Strength can be evaluated by the rule of the mixture and a particle spacing effect.

The mechanism by which nanoparticles cross the placental barrier was studied by using isotopic tracers. The abortion rates and other related data were counted and analysed in pregnant mice with different pregnancy times. Results showed that oxidised multi-walledcarbon nanotubes (oMWCNTs) crossed the placental barrier and entered the foetus body. The abortion rates in the pregnant mice depended on pregnancy times. The abortion rates in the first-time, second-time and fourth-time pregnant mice were 70%, 40% and 50%, respectively. The maternal body weight gain was inhibited until gestational ages of 13, 10 and 11 d. oMWCNTs decreased the serum progesterone level and increased the serum oestradiol level in a dose- and time-dependent manner. However, this effect decreased with gestational age. The histology and vascular endothelial growth factor/reactive oxygen species content in the placenta showed that oMWCNTs narrowed the blood vessel and decreased the number of blood vessels in the placenta.

Summary The inclusion of nanoparticles modifies a number of fundamental properties of many materials. Doping of nanoparticles in self-organized materials such as liquid crystals may be of interest for the reciprocal interaction between the matrix and the nanoparticles. Elongated nanoparticles and nanotubes can be aligned and reoriented by the liquid crystal, inducing noticeable changes in their optical and electrical properties. In this work, cells of liquid crystal doped with high aspect ratio multi-walledcarbon nanotubes have been prepared, and their characteristic impedance has been studied at different frequencies and excitation voltages. The results demonstrate alterations in the anisotropic conductivity of the samples with the applied electric field, which can be followed by monitoring the impedance evolution with the excitation voltage. Results are consistent with a possible electric contact between the coated substrates of the LC cell caused by the reorientation of the nanotubes. The reversibility of the doped system upon removal of the electric field is quite low. PMID:25821679

This work reports the design of a resistive gas sensor based on 2D mats of multi-walledcarbon nanotubes (MWCNTs) grown by aerosol-assisted chemical vapour deposition. The sensor sensitivity was optimized using chlorine as analyte by tuning both CNT network morphology and CNT electronic properties. Optimized devices, operating at room temperature, have been calibrated over a large range of concentration and are shown to be sensitive down to 27 ppb of chlorine. The as-grown MWCNT response is compared with responses of 2000 °C annealed CNTs, as well as of nitrogen-doped CNTs and CNTs functionalized with polyethyleneimine (PEI). Under chlorine exposure, the resistance decrease of as-grown and annealed CNTs is attributed to charge transfer from chlorine to CNTs and demonstrates their p-type semiconductor behaviour. XPS analysis of CNTs exposed to chlorine shows the presence of chloride species that confirms electron charge transfer from chlorine to CNTs. By contrast, the resistance of nitrogen-doped and PEI functionalized CNTs exposed to chlorine increases, in agreement with their n-type semiconductor nature. The best response is obtained using annealed CNTs and is attributed to their higher degree of crystallinity. PMID:21289407

This study evaluated the biological responses to multi-walledcarbon nanotubes (MWCNTs). Human monoblastic leukemia cells (U937) were exposed to As-grown MWCNTs and MWCNTs that were thermally treated at 1800 deg. C (HTT1800) and 2800 deg. C (HTT2800). Cell proliferation was highly inhibited by As-grown but not HTT2800. However, both As-grown and HTT1800, which include some impurities, were cytotoxic. Proteomics analysis of MWCNT-exposed cells revealed 37 protein spots on 2-dimensional electrophoresis gels that significantly changed (p < 0.05) after exposure to HTT1800 with a little iron and 20 spots that changed after exposure to HTT2800. Peptide mass fingerprinting identified 45 proteins that included heat shock protein beta-1, neutral alpha-glucosidase AB, and DNA mismatch repair protein Msh2. These altered proteins play roles in metabolism, biosynthesis, response to stress, and cell differentiation. Although HTT2800 did not inhibit cell proliferation or cause cytotoxicity in vitro, some proteins related to the response to stress were changed. Moreover, DJ-1 protein, which is a biomarker of Parkinson's disease and is related to cancer, was identified after exposure to both MWCNTs. These results show that the cytotoxicity of MWCNTs depends on their impurities, such as iron, while MWCNTs themselves cause some biological responses directly and/or indirectly in vitro. Our proteomics-based approach for detecting biological responses to nanomaterials is a promising new method for detailed safety evaluations.

Recently, various nanoscale materials, including silver (Ag) nanoparticles, have been actively studied for their capacity to effectively prevent bacterial growth. A critical challenge is to enhance the antibacterial properties of nanomaterials while maintaining their biocompatibility. The conjugation of multiple nanomaterials with different dimensions, such as spherical nanoparticles and high-aspect-ratio nanotubes, may increase the target-specific antibacterial capacity of the consequent nanostructure while retaining an optimal biocompatibility. In this study, multi-walledcarbon nanotubes (MWCNTs) were treated with a mixture of acids and decorated with Ag nanoparticles via a chemical reduction of Ag cations by ethanol solution. The synthesized Ag-MWCNT complexes were characterized by transmission electron microscopy, X-ray diffractometry, and energy-dispersive X-ray spectroscopy. The antibacterial function of Ag-MWCNTs was evaluated against Methylobacterium spp. and Sphingomonas spp. In addition, the biocompatibility of Ag-MWCNTs was evaluated using both mouse liver hepatocytes (AML 12) and human peripheral blood mononuclear cells. Finally, we determined the minimum amount of Ag-MWCNTs required for a biocompatible yet effective antibacterial treatment modality. We report that 30 μg/mL of Ag-MWCNTs confers antibacterial functionality while maintaining minimal cytotoxicity toward both human and animal cells. The results reported herein would be beneficial for researchers interested in the efficient preparation of hybrid nanostructures and in determining the minimum amount of Ag-MWCNTs necessary to effectively hinder the growth of bacteria. PMID:25336943

This study investigates therapeutic efficacy of photothermal therapy (PTT) in an orthotropic xenograft model of bone metastasis of breast cancer. The near-infrared (NIR) irradiation on Multi-WalledCarbon Nanotubes (MWNTs) resulted in a rapid heat generation which increased with the MWNTs concentration up to 100 μg/ml. MWNTs alone exhibited no toxicity, but inclusion of MWNTs dramatically decreased cell viability when combined with laser irradiation. Thermographic observation revealed that treatment with 10 μg MWNTs followed by NIR laser irradiation resulted in a rapid increase in temperature up to 73.4±11.98 °C in an intraosseous model of bone metastasis of breast cancer. In addition, MWNTs plus NIR laser irradiation caused a remarkably greater suppression of tumor growth compared with treatment with either MWNTs injection or NIR irradiation alone, significantly reducing the amount of tumor-induced bone destruction. All these demonstrate the efficacy of PTT with MWNTs for bone metastasis of breast cancer. PMID:26122018

Two multi-walledcarbon nanotube (MWCNT)-based nanohybrids, MWCNT-ZnTPP and MWCNT-TPP (TPP=5-[4-{2-(4-formylphenoxy)- ethyloxy}phenyl]-10,15,20-triphenylporphyrin, ZnTPP=5-[4-{(4-formylphenyl)ethynyl}phenyl]-10,15,20-triphenylporphinatozinc(II)), were prepared directly from pristine MWCNTs through 1,3-dipolar cycloaddition reactions. Covalent attachment of the porphyrins to the surfaces of the MWCNTs was confirmed by Fourier transform infrared spectroscopy, ultraviolet/visible absorption, fluorescence, Raman, and X-ray photoelectron spectroscopy, elemental analysis, transmission electron microscopy, and thermogravimetric analysis. Attachment of the porphyrin moieties to the surface of the MWCNTs significantly improves the solubility and ease of processing of these MWCNT-porphyrin composite materials. Z-scan studies reveal that these MWCNT-porphyrin nanohybrids exhibit enhanced nonlinear optical properties under both nanosecond and picosecond laser pulses at λ=532 nm in comparison with free MWCNTs and the free porphyrin chromophores, whereas superior optical limiting performance was displayed by MWCNT-porphyrin composite materials rather than MWCNTs/ZnTPP and MWCNTs/TPP blends, which is consistent with a remarkable accumulation effect as a result of the covalent linkage between the porphyrin and the MWCNTs. PMID:24038312

Traumatic injuries to the brain and spinal cord affect a large percentage of the world’s population. However, there are currently no effective treatments for these central nervous system (CNS) injuries. In our study, we evaluated the neuroprotective role of functionalized multi-walledcarbon nanotubes (MWCNTs) carrying brain derived neurotrophic factor (BNDF), nogo-66 receptor (NgR) and Ras homolog gene family member A (RhoA) in spinal cord injury (SCI). Our results showed that transfection into rat cortical neurons with BDNF-DNA significantly elevated the expression of BDNF both in vitro and in vivo. Meanwhile, transfection with NgR-siRNA and RhoA-siRNA resulted in an obvious down-regulation of NgR and RhoA in neuron cells and in injured spinal cords. In addition, the functionalized MWCNTs carrying BDNF-DNA, NgR-siRNA and RhoA-siRNA exhibited remarkable therapeutic effects on injured spinal cord. Taken together, our study demonstrates that functionalized MWCNTs have a potential therapeutic application on repair and regeneration of the CNS. PMID:26884846

Background Multi-walledcarbon nanotubes (MWCNTs) are widely used in many disciplines due to their unique physical and chemical properties. Therefore, some concerns about the possible human health and environmental impacts of manufactured MWCNTs are rising. We hypothesized that instillation of MWCNTs impairs pulmonary function in C57BL/6 mice due to development of lung inflammation and fibrosis. Methods MWCNTs were administered to C57BL/6 mice by oropharyngeal aspiration (1, 2, and 4 mg/kg) and we assessed lung inflammation and fibrosis by inflammatory cell infiltration, collagen content, and histological assessment. Pulmonary function was assessed using a FlexiVent system and levels of Ccl3, Ccl11, Mmp13 and IL-33 were measured by RT-PCR and ELISA. Results Mice administered MWCNTs exhibited increased inflammatory cell infiltration, collagen deposition and granuloma formation in lung tissue, which correlated with impaired pulmonary function as assessed by increased resistance, tissue damping, and decreased lung compliance. Pulmonary exposure to MWCNTs induced an inflammatory signature marked by cytokine (IL-33), chemokine (Ccl3 and Ccl11), and protease production (Mmp13) that promoted the inflammatory and fibrotic changes observed within the lung. Conclusions These results further highlight the potential adverse health effects that may occur following MWCNT exposure and therefore we suggest these materials may pose a significant risk leading to impaired lung function following environmental and occupational exposures. PMID:21851604

In this paper, we propose strain-sensitive thin films based on chemically reduced graphene oxide (GO) and multi-walledcarbon nanotubes (MWCNTs) without adding any further surfactants. In spite of the insulating properties of the thin-film-based GO due to the presence functional groups such as hydroxyl, epoxy, and carbonyl groups in its atomic structure, a significant enhancement of the film conductivity was reached by chemical reduction with hydro-iodic acid. By optimizing the MWCNT content, a significant improvement of electrical and mechanical thin film sensitivity is realized. The optical properties and the morphology of the prepared thin films were studied using ultraviolet-visible spectroscopy (UV-Vis) and scanning electron microscope (SEM). The UV-Vis spectra showed the ability to tune the band gap of the GO by changing the MWCNT content, whereas the SEM indicated that the MWCNTs were well dissolved and coated by the GO. Investigations of the piezoresistive properties of the hybrid nanocomposite material under mechanical load show a linear trend between the electrical resistance and the applied strain. A relatively high gauge factor of 8.5 is reached compared to the commercial metallic strain gauges. The self-assembled hybrid films exhibit outstanding properties in electric conductivity, mechanical strength, and strain sensitivity, which provide a high potential for use in strain-sensing applications. PMID:26732277

There is a current interest in reducing the in vivo toxicity testing of nanomaterials in animals by increasing toxicity testing using in vitro cellular assays; however, toxicological results are seldom concordant between in vivo and in vitro models. This study compared global multi-walledcarbon nanotube (MWCNT)-induced gene expression from human lung epithelial and microvascular endothelial cells in monoculture and coculture with gene expression from mouse lungs exposed to MWCNT. Using a cutoff of 10% false discovery rate and 1.5 fold change, we determined that there were more concordant genes (gene expression both up- or downregulated in vivo and in vitro) expressed in both cell types in coculture than in monoculture. When reduced to only those genes involved in inflammation and fibrosis, known outcomes of in vivo MWCNT exposure, there were more disease-related concordant genes expressed in coculture than monoculture. Additionally, different cellular signaling pathways are activated in response to MWCNT dependent upon culturing conditions. As coculture gene expression better correlated with in vivo gene expression, we suggest that cellular cocultures may offer enhanced in vitro models for nanoparticle risk assessment and the reduction of in vivo toxicological testing. PMID:25511174

This study presents a novel method for preparing multi-walledcarbon nanotubes (MWNTs) grafted with a poly(2-hydroxyethyl methacrylate) (HEMA)-silver complex (CNTs-HEMA-Ag complex) through plasma-induced grafting polymerization. The characteristics of the MWNTs after being grafted with HEMA polymer are monitored by Fourier transform infrared (FT-IR) spectroscopy. The chelating groups in the HEMA polymer grafted on the surface of the CNTs-HEMA are the coordination sites for chelating silver ions, and are further used as nanotemplates for the growing of Ag nanoparticles (quantum dots). Transmission electron microscopy (TEM) reveals that the particle size of Ag nanoparticles on the CNT surfaces increases with the Ag+ chelating concentration, reaction time, and reaction temperature. Moreover, the crystalline phase of Ag nanoparticles is identified by using x-ray diffraction (XRD). In addition, high-resolution x-ray photoelectron spectroscopy (XPS) is used to characterize the functional groups on the surface of the MWNTs after chemical modification through plasma treatment; it demonstrates that the growing amount of the Ag nanoparticles on the nanotubes increases with the Ag+ chelating concentration due to the blocking effect of the Ag particles forming on the MWNTs.

The multiphase approach was adapted to enhance the electromagnetic interference (EMI) shielding effectiveness (SE) of polyaniline (PANI) based nanocomposites. The natural graphite flakes (NGF) incorporated modified PANI was used for the development of multi-walledcarbon nanotubes (MWCNTs) based nanocomposites. In PANINGF-MWCNTs composites, multilayer graphene was synthesized in situ by ball milling. The resultant PANINGF-MWCNTs nanocomposites were characterized by different techniques. It was revealed from the transmission electron microscope (TEM) observation that in situ derived multilayer graphene acts as a bridge between PANI and MWCNTs, and plays a significant role for improving the properties of multiphase nanocomposites. It was observed that EMI-SE increases with increasing the MWCNTs content from 1 to 10 wt% in the multiphase nanocomposites. The maximum value of total EMI-SE was -98 dB of nanocomposite with 10 wt% of MWCNTs content. The high value of EMI-SE is dominated by the absorption phenomenon which is due to the collective effect of increase in space charge polarization and decrease in carrier mobility. The decrease in carrier mobility has a positive effect on the shore hardness value due to the strong interaction between the reinforcing constituent in multiphase nanocomposites. As a consequence, shore hardness increases from 56 to 91 at 10 wt% of MWCNTs. PMID:24264356

Multi-wallcarbon nanotubes (MWCNTs)-3 mol% yttria-stabilized zirconia (3Y-TZP) (MWCNTs-3Y-TZP) composite was prepared by spark plasma sintering. The complex permittivities of the composite have been measured in the Ku-band range (12.4-18 GHz) and it is found that both the real and imaginary permittivities of the composite increase with the increasing content of MWCNTs. The effect of the content of MWCNTs on the electromagnetic interference (EMI) shielding effectiveness (SE) of the composite has been evaluated, and it is found that the EMI SE of the composite increases with the increasing content of MWCNTs. An EMI SE value as high as 25-30 dB has been achieved in the Ku-band range for the composite with 9 wt% content of MWCNTs, indicating that the MWCNTs-3Y-TZP composite can be used as an effective EMI shielding material. PMID:21828667

A single step approach for the synthesis of multi-walledcarbon nanotubes filled with Ni nanowires (Ni-MWCNTs) and decorated with Ni nanoparticles has been illustrated. The MWCNTs are grown by a PECVD-sputtering hybrid process at the low temperature of 450 °C having an average diameter of 55 ± 6 nm and length of 1.35 ± 0.08 µm. Thin Ni films of the thickness 10 nm have been used, which act as a catalyst as well as a source material for the filling of MWCNTs with Ni nanowires, whereas sputtering of Ni is the source of decorated Ni particles. This process facilitates the growth of aligned MWCNTs filled with Ni nanowires and also decorated with Ni nanoparticles on the walls. Magnetic properties of the Ni filled and decorated MWCNTs are measured using a vibrating sample magnetometer. Magnetic hysteresis loops of Ni containing MWCNTs show ferromagnetic behavior. These Ni-MWCNTs shows coercivity of 135 Oe, which is significantly greater than that of the bulk Ni at room temperature. The magnetic property measurement reveals that the coercivity of the as grown MWCNTs is dependent on the size and content of Ni. Thus, a novel method has been demonstrated for the synthesis of ferromagnetic Ni-MWCNT which has potential applications in various fields.

The impact of vectorial magnetic field effects on electrical conductivity and nonlinear optical transmittance exhibited by multi-wallcarbon nanotubes was studied. The samples were synthetized by an aerosol pyrolysis processing route in a thin film form. Optical signals in a two-wave mixing configuration allowed us to identify two orthogonal directions of propagation for a magnetic field travelling through the nanomaterials studied. A selective modification in optical absorption was considered to be induced by magnetic perturbations in the sample. Standard optical Kerr gate measurements were carried out for exploring the third order nonlinear optical behavior of the film. A capacitive effect influenced by optical and magnetic excitations was distinguished to be characteristic of the sample. Magneto-quantum conductivity sensitive to the direction of an external magnetic field interacting with the tubes was analyzed. Magnetically-induced changes in electronic band parameters seem to be the main responsible for the optical and electrical modulation observed in the nanostructures. Immediate applications for developing magneto-optical and magneto-electrical functions can be contemplated. PMID:27557232

Biomedical applications of carbon nanotubes (CNTs) often involve improving their hydrophilicity and dispersion in biological media by modifying them through noncovalent or covalent functionalization. However, the potential adverse effects of surface-functionalized CNTs have not been well characterized. In this study, we functionalized multi-walled CNTs (MWCNTs) via carboxylation, to produce MWCNTs-COOH, and via poly (ethylene glycol) linking, to produce MWCNTs-PEG. We used these functionalized MWCNTs to study the effect of surface functionalization on MWCNTs-induced toxicity to macrophages, and elucidate the underlying mechanisms of action. Our results revealed that MWCNTs-PEG were less cytotoxic and were associated with less apoptotic cell death of macrophages than MWCNTs-COOH. Additionally, MWCNTs-PEG induced less generation of reactive oxygen species (ROS) involving less activation of NADPH oxidase compared with MWCNTs-COOH, as evidenced by membrane translocation of p47phox and p67phox in macrophages. The less cytotoxic and apoptotic effect of MWCNTs-PEG compared with MWCNTs-COOH resulted from the lower cellular uptake of MWCNTs-PEG, which resulted in less activation of oxidative stress-responsive pathways, such as p38 mitogen-activated protein kinases (MAPK) and nuclear factor (NF)-κB. These results demonstrate that surface functionalization of CNTs may alter ROS-mediated cytotoxic and apoptotic response by modulating apoptotic signaling pathways. Our study thus provides new insights into the molecular basis for the surface properties affecting CNTs toxicity. PMID:23755279

The aim of this study was to develop multi-walledcarbon nanotubes (MWCNT) which were covalently conjugated with transferrin by carbodiimide chemistry and loaded with docetaxel as a model drug for effective treatment of lung cancer in comparison with the commercial docetaxel injection (Docel™). d-Alpha-tocopheryl polyethylene glycol 1000 succinate (TPGS) was used as amphiphilic surfactant to improve the aqueous dispersity and biocompatibility of MWCNT. Human lung cancer cells (A549 cells) were employed as an in-vitro model to access cellular uptake, cytotoxicity, cellular apoptosis, cell cycle analysis, and reactive oxygen species (ROS) of the docetaxel/coumarin-6 loaded MWCNT. The cellular uptake results of transferrin conjugated MWCNT showed higher efficiency in comparison with free C6. The IC50 values demonstrated that the transferrin conjugated MWCNT could be 136-fold more efficient than Docel™ after 24h treatment with the A549 cells. Flow cytometry analysis confirmed that cancerous cells appeared significantly (P<0.05) in the sub-G1 phase for transferrin conjugated MWCNT in comparison with Docel™. Results of transferrin conjugated MWCNT have showed better efficacy with safety than Docel™. PMID:27287127

Alginate is a hydrogel commonly used for cell culture by ionically crosslinking in the presence of divalent Ca(2+) ions. However these alginate gels are mechanically unstable, not permitting their use as scaffolds to engineer robust biological bone, breast, cardiac or tumor tissues. This issue can be addressed via encapsulation of multi-walledcarbon nanotubes (MWCNT) serving as a reinforcing phase while being dispersed in a continuous phase of alginate. We hypothesized that adding functionalized MWCNT to alginate, would yield composite gels with distinctively different mechanical, physical and biological characteristics in comparison to alginate alone. Resultant MWCNT-alginate gels were porous, and showed significantly less degradation after 14 days compared to alginate alone. In vitro cell-studies showed enhanced HeLa cell adhesion and proliferation on the MWCNT-alginate compared to alginate. The extent of cell proliferation was greater when cultured atop 1 and 3 mg/ml MWCNT-alginate; although all MWCNT-alginates lead to enhanced cell cluster formation compared to alginate alone. Among all the MWCNT-alginates, the 1 mg/ml gels showed significantly greater stiffness compared to all other cases. These results provide an important basis for the development of the MWCNT-alginates as novel substrates for cell culture applications, cell therapy and tissue engineering. PMID:27578567

In this study, we propose a multi-walledcarbon nanotube epoxy composite sensor for force and pressure sensing in the range of 50 N–2 kN. A manufacturing procedure, including material preparation and deposition techniques, is proposed. The electrode dimensions and the layer thickness were optimized by the finite element method. Temperature compensation is realized by four nanocomposites elements, where only two elements are exposed to the measurand. In order to investigate the influence of the filler contents, samples with different compositions were prepared and investigated. Additionally, the specimens are characterized by cyclical and stepped force/pressure loads or at defined temperatures. The results show that the choice of the filler content should meet a compromise between sensitivity, temperature influence and noise behavior. At constant temperature, a force of at least 50 N can be resolved. The measurement error due to the temperature influence is 150 N in a temperature range of −20°C−50°C. PMID:25985160

Thermal conductivity, viscosity, and stability of nanofluids containing multi-walledcarbon nanotubes (MWCNTs) stabilized by cationic chitosan were studied. Chitosan with weight fraction of 0.1%, 0.2 wt%, and 0.5 wt% was used to disperse stably MWCNTs in water. The measured thermal conductivity showed an enhancement from 2.3% to 13% for nanofluids that contained from 0.5 wt% to 3 wt% MWCNTs (0.24 to 1.43 vol %). These values are significantly higher than those predicted using the Maxwell's theory. We also observed that the enhancements were independent of the base fluid viscosity. Thus, use of microconvection effect to explain the anomalous thermal conductivity enhancement should be reconsidered. MWCNTs can be used either to enhance or reduce the fluid base viscosity depending on the weight fractions. In the viscosity-reduction case, a reduction up to 20% was measured by this work. In the viscosity-enhancement case, the fluid behaved as a non-Newtonian shear-thinning fluid. By assuming that MWCNT nanofluids behave as a generalized second grade fluid where the viscosity coefficient depends upon the rate of deformation, a theoretical model has been developed. The model was found to describe the fluid behavior very well.

The specific features of changes in the electronic structure of multi-walledcarbon nanotubes (MWCNTs) due to the interaction with an amorphous tin oxide in the SnO x /MWCNT composite formed by magnetron sputtering have been investigated using X-ray spectroscopy. It has been shown that the formation of chemical bonds responsible for significant changes in the local and electronic structures of the outer layers of MWCNTs occurs at the boundaries of the "amorphous oxide/MWCNT" contacts. The vacuum annealing of the composite leads to the disturbance of the chemical interaction at interfaces of the composite and to a partial recovery of the local structure of the outer layers of MWCNTs. A decrease in the amount of oxygen in the tin oxide under vacuum annealing conditions causes an increase in the number of unpaired Sn 5 s electrons, which, in turn, enhances the charge transfer through the interfaces in the composite and leads to a splitting of the π*-subsystem of the outer layers of MWCNTs.

In this paper, nickel oxide (NiO) nanoparticles have been fabricated using wet method and deposited on the surface of multi-walledcarbon nanotube (MWCNT). To do so, functional groups were introduced on the surface of MWCNTs by treating with concentrated nitric acid. Nickel oxide nanoparticles were formed on the surface of functionalized MWCNTs by incipient wetness impregnation of nickel nitrate, and the resultant product was calcinated in air atmosphere. Characteristics of the NiO/MWCNT were examined by various techniques, for example, Fourier transform spectroscopy (FTIR), X-ray diffraction analysis (XRD), transmission electron microscopy (TEM), thermogravimetric analyzer (TGA), and nitrogen adsorption-desorption isothermal as well as vibrating sample magnetometer (VSM). The FTIR spectra showed that carboxyl and hydroxyl functional groups existed on the surface of MWNTs after modification by concentrated nitric acid. The pattern of XRD indicated that MWNTs and nickel oxide nanoparticles coexisted in the NiO/MWCNT sample. The TEM images revealed that the NiO nanoparticles were distributed on the surface of the MWNTs, with the size ranging from 5 to 60 nm. Thermogravimetric analysis proved that NiO content decorated on MWCNTs was 80 and 15 wt%. The results of the Brunauer-Emmett-Teller (BET) data showed that the slight increment in the specific surface areas and porosities in the presence of the NiO nanoparticles on the surface of CNT.

We report the first attempt to prepare a flexoelectric nanogenerator consisting of direct-grown piezoelectrics on multi-walledcarbon nanotubes (mwCNT). Direct-grown piezoelectrics on mwCNTs are formed by a stirring and heating method using a Pb(Zr0.52Ti0.48)O3 (PZT)-mwCNT precursor solution. We studied the unit cell mismatch and strain distribution of epitaxial PZT nanoparticles, and found that lattice strain is relaxed along the growth direction. A PZT-mwCNT nanogenerator was found to produce a peak output voltage of 8.6 V and an output current of 47 nA when a force of 20 N is applied. Direct-grown piezoelectric nanogenerators generate a higher voltage and current than simple mixtures of PZT and CNTs resulting from the stronger connection between PZT crystals and mwCNTs and an enhanced flexoelectric effect caused by the strain gradient. These experiments represent a significant step toward the application of nanogenerators using piezoelectric nanocomposite materials. PMID:27406631

Zirconia/multi-walledcarbon nanotube (ZrO{sub 2}/MWCNT) nanocomposite was prepared by hydrothermal treatment of MWCNTs in ZrOCl{sub 2}.8H{sub 2}O aqueous solution. The morphology and structure of the synthesized ZrO{sub 2}/MWCNT nanocomposite were characterized by transmission electron microscopy and X-ray diffraction analysis. It was found that ZrO{sub 2} nanoparticles homogeneously distributed on the sidewall of MWCNTs. Myoglobin (Mb), as a model protein to investigate the nanocomposite, was immobilized on ZrO{sub 2}/MWCNT nanocomposite. Ultraviolet-visible spectroscopy and electrochemical measurements showed that the nanocomposite could retain the bioactivity of the immobilized Mb to a large extent. The Mb immobilized in the composite showed excellent direct electrochemistry and electrocatalytic activity to the reduction of hydrogen peroxide (H{sub 2}O{sub 2}). The linear response range of the biosensor to H{sub 2}O{sub 2} concentration was from 1.0 to 116.0 {mu}M with the limit of detection of 0.53 {mu}M (S/N = 3). The ZrO{sub 2}/MWCNT nanocomposite provided a good biocompatible matrix for protein immobilization and biosensors preparation.

This paper investigates the interaction of ten diverse biomolecules with surfactant detached Multi-WalledCarbon Nanotubes (MWCNTs) using multiple spectroscopic methods. Declining fluorescence intensity of biomolecules in combination with the hyperchromic effect in UV-Visible spectra confirmed the existence of the ground state complex formation. Quenching mechanism remains static and non-fluorescent. 3D spectral data of biomolecules suggested the possibilities of disturbances to the aromatic microenvironment of tryptophan and tyrosine residues arising out of CNTs interaction. Amide band Shifts corresponding to the secondary structure of biomolecules were observed in the of FTIR and FT-Raman spectra. In addition, there exists an increased Raman intensity of tryptophan residues of biomolecules upon interaction with CNTs. Hence, the binding of the aromatic structures of CNTs with the aromatic amino acid residues, in a particular, tryptophan was evidenced. Far UV Circular spectra have showed the loss of alpha-helical contents in biomolecules upon interaction with CNTs. Near UV CD spectra confirmed the alterations in the tryptophan positions of the peptide backbone. Hence, our results have demonstrated that the interaction of biomolecules with OH-MWCNTs would involve binding cum structural changes and alteration to their aromatic micro-environment. PMID:25707749

Biocompatibility of nanoparticles depends on their binding behavior with biomolecules. Herein, we have reported the interaction of three different biological macromolecules such as hemoglobin, gamma globulin and transferrin with hydroxyl group functionalized Multi-WalledCarbon Nanotubes (OH-MWCNTs). Multiple spectroscopic methods were utilized to identify the binding cum structural changes in biomolecules upon their interaction. Hyperchromic effect observed in the UV-visible spectra, and the quenching behavior from fluorescence emission evidences the existence of bio-nanotube complex formation. Synchronous and three-dimensional fluorescence spectra of biomolecules, in correspondence with Trp and Tyr residues showed the possible disturbance towards their aromatic micro-environment. Changes observed in the FTIR and FT-Raman amide bands, and amino acid residue position of biomolecules upon interaction with CNTs showed the possible effect towards their secondary structure. Further studies with CD spectroscopy indicated the loss of alpha-helical structures quantitatively. The study remains significant in evaluating the biosafety profile of functionalized MWCNTs for their in vivo biomedical applications. PMID:26432959

Asbestos exposure is considered a social burden by causing mesothelioma. Despite the use of synthetic materials, multi-walledcarbon nanotubes (MWCNTs) are similar in dimension to asbestos and produce mesothelioma in animals. The role of inflammatory cells in mesothelial carcinogenesis remains unclear. Here, we evaluated the differences in inflammatory cell responses following exposure to these fibrous materials using a luminometer and L-012 (8-amino-5-chloro-7-phenylpyrido[3,4-d]pyridazine-1,4-(2H,3H) dione) to detect reactive oxygen species (ROS). Rat peripheral blood or RAW264.7 cells were used to assess the effects on neutrophils and macrophages, respectively. Crocidolite and amosite induced significant ROS generation by neutrophils with a peak at 10 min, whereas that of chrysotile was ~25% of the crocidolite/amosite response. MWCNTs with different diameters (~15, 50, 115 and 145 nm) and different carcinogenicity did not induce significant ROS in peripheral blood. However, the MWCNTs induced a comparable amount of ROS in RAW264.7 cells to that following asbestos treatment. The peaks for MWCNTs (0.5–1.5 h) were observed earlier than those for asbestos (1–5 h). Apocynin and superoxide dismutase significantly inhibited ROS generation for each fiber, suggesting an involvement of NADPH oxidase and superoxide. Thus, asbestos and MWCNTs induce different oxidative responses in inflammatory cells, indicating the importance of mesothelial cell evaluation for carcinogenesis. PMID:25759516

Studies of the neurobehavioral effects of carbon nanomaterials, particularly those of multi-walledcarbon nanotubes (MWCNTs), have concentrated on cognitive effects, but data are scarce. The aim of this study was to assess the influence of MWCNTs on a number of higher nervous system functions of Wistar rats. For a period of 10 days, two experimental groups were fed with MWCNTs of different diameters (MWCNT-1 group, 8–10 nm; MWCNT-2 group, 18–20 nm) once a day at a dosage of 500 mg/kg. In the open-field test, reductions of integral indications of researching activity were observed for the two MWCNT-treated groups, with a parallel significant (P<0.01) increase in stress levels for these groups compared with the untreated control group. In the elevated plus-maze test, integral indices of researching activity in the MWCNT-1 and MWCNT-2 groups reduced by day 10 by 51 and 62%, respectively, while rat stress levels remained relatively unchanged. In the universal problem solving box test, reductions in motivation and energy indices of researching activity were observed in the two experimental groups. Searching activity in the MWCNT-1 group by day 3 was reduced by 50% (P<0.01) and in the MWCNT-2 group the relevant reduction reached 11.2%. By day 10, the reduction compared with controls, was 64% (P<0.01) and 58% (P<0.01) for the MWCNT-1 and MWCNT-2 groups, respectively. In conclusion, a series of specific tests demonstrated that MWCNT-treated rats experienced a significant reduction of some of their cognitive abilities, a disturbing and worrying finding, taking into consideration the continuing and accelerating use of carbon nanotubes in medicine and science. PMID:27588053

A simple and novel method, water-assisted chemical vapor deposition (CVD) was developed to functionalize multi-walledcarbon nanotubes (MWCNTs) during the synthesis process. The functionalized MWCNTs were characterized using Raman spectroscopy, XPS, TGA, NH{sub 3}-TPD, SEM and HR-TEM. It was found that new defects are introduced and the amount of acidic groups is increased on the MWCNT surface during the water-assisted CVD process. The amount of C-OH and C-O group on the MWCNT surface is found to be increased from 21.1% to 42% with water vapor assistance. Density functional theory (DFT) was employed to study the chemical behavior of water vapor molecule on the catalyst particle surface of Ni(1 1 1) cluster. Based on the experimental and DFT simulation results, a mechanism for functionalization of MWCNTs by water-assisted CVD is proposed. - Graphical abstract: Water is adsorbed and activated on Ni surface, then dissociated into OH and O species, followed by part of OH and O species desorbed from the surface. Finally, the desorbed OH and O species oxidize the unsaturated carbon atoms of carbon nanotubes, form defects and oxygen-containing groups. Highlights: Black-Right-Pointing-Pointer MWCNTs were functionalized by water-assisted CVD method. Black-Right-Pointing-Pointer Defects and weak-medium acidic sites were created on the MWCNT sidewalls. Black-Right-Pointing-Pointer Oxygen-containing groups in functionalized MWCNT were increased from 21.1% to 42%. Black-Right-Pointing-Pointer A mechanism for the influence of water vapor on MWCNTs was proposed.

The world-wide production of carbon nanotubes (CNTs) has increased substantially in the last decade, leading to occupational exposures. There is a paucity of exposure data of workers involved in the commercial production of CNTs. The goals of this study were to assess personal exposure to multi-walledcarbon nanotubes (MWCNTs) during the synthesis and handling of MWCNTs in a commercial production facility and to link these exposure levels to specific activities. Personal full-shift filter-based samples were collected, during commercial production and handling of MWCNTs, R&D activities, and office work. The concentrations of MWCNT were evaluated on the basis of EC concentrations. Associations were studied between observed MWCNT exposure levels and location and activities. SEM analyses showed MWCNTs, present as agglomerates ranging between 200nm and 100 µm. Exposure levels of MWCNTs observed in the production area during the full scale synthesis of MWCNTs (N = 23) were comparable to levels observed during further handling of MWCNTs (N = 19): (GM (95% lower confidence limit-95% upper confidence limit)) 41 μg m(-3) (20-88) versus 43 μg m(-3) (22-86), respectively. In the R&D area (N = 11) and the office (N = 5), exposure levels of MWCNTs were significantly (P < 0.05) lower: 5 μg m(-3) (2-11) and 7 μg m(-3) (2-28), respectively. Bagging, maintenance of the reactor, and powder conditioning were associated with higher exposure levels in the production area, whereas increased exposure levels in the R&D area were related to handling of MWCNTs powder. PMID:26613611

A multi-wallcarbon nanotube (MWCNT) product Mitsui MWNT-7 is a mixture of dispersed single fibers and their agglomerates/aggregates. In rodents, installation of such mixture induces inflammatory lesions triggered predominantly by the aggregates/agglomerates at the level of terminal bronchiole of the lungs. In human, however, pulmonary toxicity induced by dispersed single fibers that reached the lung alveoli is most important to assess. Therefore, a method to generate aerosol predominantly consisting of dispersed single fibers without changing their length and width is needed for inhalation studies. Here, we report a method (designated as Taquann method) to effectively remove the aggregate/agglomerates and enrich the well-dispersed singler fibers in dry state without dispersant and without changing the length and width distribution of the single fibers. This method is base on two major concept; liquid-phase fine filtration and critical point drying to avoid re-aggregation by surface tension. MWNT-7 was suspended in Tert-butyl alcohol, freeze-and-thawed, filtered by a vibrating 25 µm mesh Metallic Sieve, snap-frozen by liquid nitrogen, and vacuum-sublimated (an alternative method to carbon dioxide critical point drying). A newly designed direct injection system generated well-dispersed aerosol in an inhalation chamber. The lung of mice exposed to the aerosol contained single fibers with a length distribution similar to the original and the Taquann-treated sample. Taquann method utilizes inexpensive materials and equipments mostly found in common biological laboratories, and prepares dry powder ready to make well-dispersed aerosol. This method and the chamber with direct injection system would facilitate the inhalation toxicity studies more relevant to human exposure. PMID:23824017

The porosity and microstructure of a Portland cement-multi-walledcarbon nanotube composite were investigated. Multi-walledcarbon nanotubes (CNTs), up to 1 wt.% of cement, synthesized by infusion chemical vapor deposition, and Portland cement type I (PC) were used to produce pastes with a water to cement ratio of 0.5. Mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM) were used to characterize Portland cement-CNTs systems. MIP analysis of the results indicates that total porosity of the mixes with CNTs was found to decrease with increasing CNTs content. Moreover, an important effect of additional CNTs was a reduction in the number of mesopores, while SEM technique showed dispersion of CNTs between the hydration phases of Portland cement pastes.

We report high-temperature (300-1120 K) magnetic properties of Fe and Fe3O4 nanoparticles embedded in multi-walledcarbon nanotubes. We unambiguously show that the magnetic moments of Fe and Fe3O4 nanoparticles are seemingly enhanced by a factor of about 3 compared with what they would be expected to have for free (unembedded) magnetic nanoparticles. What is more intriguing is that the enhanced moments were completely lost when the sample was heated up to 1120 K and the lost moments at 1120 K were completely recovered through several thermal cycles below 1020 K. The anomalous thermal hysteresis of the high-field magnetic moments is unlikely to be explained by existing physical models except for the high-field paramagnetic Meissner effect due to the existence of ultrahigh temperature superconductivity in the multi-walledcarbon nanotubes.

A conducting composite prepared by dispersing multi-walledcarbon nanotubes (MWCNTs) into a host matrix consisting of Nafion, electrochemically doped with copper, has been prepared, characterized and used to modify one of the gold electrodes of simply designed electrochemical cells having copier grade transparency sheets as substrates. Electrical measurements performed in deionized water show that the Au/Nafion/Au-MWCNTs–Nafion:Cu cells can be successfully used in order to detect the presence of p-aminophenol (PAP) in water, without the need for any supporting electrolyte. The intensity of the redox peaks arising when PAP is added to deionized water is found to be linearly related to the analyte in the range from 0.2 to 1.6 μM, with a detection limit of 90 nM and a sensitivity of 7 μA·(μM−1)·cm−2. PMID:24854357

Objective Instillation of multi-walledcarbon nanotubes (MWCNTs) in C57BL/6 mice results in decrements of pulmonary function specifically characterized by increases in airway resistance. In this study, we examined possible mechanisms responsible for these alterations following MWCNT exposure, including the roles of IL-33 and chronic inflammation. Materials and Methods To elucidate the role of IL-33, we assessed lung histology and pulmonary function in C57BL/6 and IL-33−/− mice 30 days following MWCNT instillation. In addition, the impact of MWCNT instillation on airway hyperresponsiveness (AHR) was assessed by methacholine challenges of C57BL/6 and IL-33−/− mice. To further understand the mechanisms by which MWCNTs may increase airway constriction, C57BL/6 mice were treated with aerosolized albuterol or injected with multiple doses of methylprednisolone via intra-peritoneal injections prior to the assessment of MWCNT-induced changes in pulmonary function. Results Total cell count, macrophages, and neutrophils were increased in the lavage fluid of C57BL/6 mice, but not in IL-33−/− mice, following MWCNT exposure. C57BL/6 mice displayed increased inflammation and fibrosis located proximal to the airways which was absent in IL-33−/− mice. Aerosolized methacholine increased parameters of airway resistance (R and Rn) in a dose-dependent manner in all groups, with MWCNT-instilled C57BL/6 mice responding more robustly compared to controls, while no differences were found in IL-33−/− mice due to MWCNT exposure. Treatment with methylprednisolone reduced both the MWCNT-induced histopathological changes and increases in R and Rn in C57BL/6 mice. Conclusion These findings suggest that IL-33 and chronic inflammation in general are critical in the pulmonary toxicity induced by MWCNT resulting in modified pulmonary function. PMID:24502429

In this work, technetium-99 (99mTc) was used as the radiolabeling isotope to study the biodistribution of oxidized multi-walledcarbon nanotubes (oMWCNTs) and/or nanodiamonds (NDs) in mice after intravenous administration. The histological impact of non-radiolabeled oMWCNTs or NDs was investigated in comparison to the co-exposure groups. 99mTc-labeled nanomaterials had high stability in vivo and fast clearance from blood . After a single injection of oMWCNTs, the highest distribution was found in the lungs, with lower uptake in the liver/spleen. As for NDs injected alone, high distribution in the liver, spleen, and lungs was observed right after. However, uptake in the lungs was decreased obviously after 24 h, while high accumulation in the liver or spleen continued. After co-injection of oMWCNTs and NDs, oMWCNTs significantly affected the distribution pattern of NDs in vivo. Meanwhile, the increasing dose of oMWCNTs decreased the hepatic and splenic accumulation of NDs and gradually increased lung retention. On the contrary, the NDs had no significant effects on the distribution of oMWCNTs in mice. Histological photographs showed that oMWCNTs were mainly captured by lung macrophages, and NDs were located in the bronchi and alveoli after co-administration. oMWCNTs and NDs had different modes of micro-cells. In conclusion, the behavior and fate of NDs in mice depended strongly on oMWCNTs, but NDs had a small influence on the biodistribution and excretion pattern of oMWCNTs.

Background Multi-walledcarbon nanotubes (MWCNT) are new manufactured nanomaterials with a wide spectrum of commercial applications. The durability and fiber-like dimensions (mean length 3.9 μm long × 49 nm diameter) of MWCNT suggest that these fibers may migrate to and have toxicity within the pleural region. To address whether the pleura received a significant and persistent exposure, C57BL/6J mice were exposed by pharyngeal aspiration to 10, 20, 40 and 80 μg MWCNT or vehicle and the distribution of MWCNT penetrations determined at 1, 7, 28 and 56 days after exposure. Following lung fixation and sectioning, morphometric methods were used to determine the distribution of MWCNT and the number of MWCNT fiber penetrations of three barriers: alveolar epithelium (alveolar penetrations), the alveolar epithelium immediately adjacent to the pleura (subpleural tissue), and visceral pleural surface (intrapleural space). Results At 1 day 18%, 81.6% and 0.6% of the MWCNT lung burden was in the airway, the alveolar, and the subpleural regions, respectively. There was an initial, high density of penetrations into the subpleural tissue and the intrapleural space one day following aspiration which appeared to decrease due to clearance by alveolar macrophages and/or lymphatics by day 7. However, the density of penetrations increased to steady state levels in the subpleural tissue and intrapleural from day 28 - 56. At day 56 approximately 1 in every 400 fiber penetrations was in either the subpleural tissue or intrapleural space. Numerous penetrations into macrophages in the alveolar airspaces throughout the lungs were demonstrated at all times but are not included in the counts presented. Conclusions The results document that MWCNT penetrations of alveolar macrophages, the alveolar wall, and visceral pleura are both frequent and sustained. In addition, the findings demonstrate the need to investigate the chronic toxicity of MWCNT at these sites. PMID:20920331

Gelatin composite films were prepared from gelatin solutions (10% w/v) containing multi-walledcarbon nanotubes (MWCNT, 0.5, 1, 1.5, and 2% w/w gelatin) as nanofiller. The water solubility, water swelling, water uptake, water vapor permeability (WVP), mechanical, and antibacterial properties of the films were examined. Water solubility, water swelling, water uptake, and WVP for gelatin films were 45 ± 1%, 821 ± 42%, 45 ± 1.1%, and 0.4 ± 0.022 g mm/m2 kPa h, respectively. Incorporation of MWCNT caused a significant decrease in water solubility, water swelling, water uptake, and WVP. Gelatin/MWCNT films containing 1–1.5% MWCNT showed the lowest water vapor transmission. Tensile strength, elongation at break, and Young's modulus for gelatin films were 13.4 ± 1.2 MPa, 95 ± 5%, and 45.4 ± 7 MPa, respectively. Incorporation of MWCNT caused a significant increase in tensile strength and decrease in the elongation at break. The largest mechanical strength was found at 1.5% MWCNT. All gelatin/MWCNT films showed significant antibacterial activities against both gram-positive and gram-negative bacteria. Our results suggest that the gelatin/MWCNT composites films could be used as a very attractive alternative to traditional materials for different biomedical and food applications. PMID:24804066

Activated multi-walledcarbon nanotubes (A-MWCNTs) were prepared using a chemical activation method to obtain well-developed pore structures for use as hydrogen storage materials. The microstructure and crystallinity of the A-MWCNTs were evaluated by X-ray diffraction and Fourier transform Raman spectroscopy. The textural properties of the A-MWCNTs were investigated by nitrogen gas sorption analysis at 77 K. The hydrogen storage capacity of the A-MWCNTs was evaluated at 77 K and 1 bar. The results showed that the specific surface area of the MWCNTs increased from 327 to 495 m{sup 2}/g as the activation temperature was increased. The highest hydrogen storage capacity was observed in the A-MWCNTs sample activated at 900 Degree-Sign C (0.54 wt%). This was attributed to it having the narrowest microporosity, which is a factor closely related to the hydrogen storage capacity. This shows that the hydrogen storage behaviors depend on the pore volume. Although a high pore volume is desirable for hydrogen storage, it is also severely affected if the pore size in the A-MWCNTs for the hydrogen molecules is suitable for creating the activation process. Highlights: Black-Right-Pointing-Pointer The AT-800 and AT-900 samples were prepared by a chemical activation method at activation temperature of 800 and 900 Degree-Sign C, respectively. Black-Right-Pointing-Pointer The AT-900 sample has the narrowest peak in comparison with the AT-800 sample, resulting from the overlap of the two peaks (Peak I and Peak II). Black-Right-Pointing-Pointer This overlapping effect is due to the newly created micropores or shrinkages of pores in Peak II. So, these determining characteristics are essential for designing materials that are suitable for molecular hydrogen storage.

The development of nanotechnology has increased the risk of exposure to types of particles other than combustion-derived particles in the environment, namely, industrial nanomaterials. On the other hand, patients with bronchial asthma are sensitive to inhaled substances including particulate matters. This study examined the effects of pulmonary exposure to a type of nano-sized carbon nanotube (multi-walled nanotubes: MWCNT) on allergic airway inflammation in vivo and their cellular mechanisms in vitro. In vivo, ICR mice were divided into 4 experimental groups. Vehicle, MWCNT (50 {mu}g/animal), ovalbumin (OVA), and OVA + MWCNT were repeatedly administered intratracheally. Bronchoalveolar lavage (BAL) cellularity, lung histology, levels of cytokines related to allergic inflammation in lung homogenates/BAL fluids (BALFs), and serum immunoglobulin levels were studied. Also, we evaluated the impact of MWCNT (0.1-1 {mu}g/ml) on the phenotype and function of bone marrow-derived dendritic cells (DC) in vitro. MWCNT aggravated allergen-induced airway inflammation characterized by the infiltration of eosinophils, neutrophils, and mononuclear cells in the lung, and an increase in the number of goblet cells in the bronchial epithelium. MWCNT with allergen amplified lung protein levels of Th cytokines and chemokines compared with allergen alone. MWCNT exhibited adjuvant activity for allergen-specific IgG{sub 1} and IgE. MWCNT significantly increased allergen (OVA)-specific syngeneic T-cell proliferation, particularly at a lower concentration in vitro. Taken together, MWCNT can exacerbate murine allergic airway inflammation, at least partly, via the promotion of a Th-dominant milieu. In addition, the exacerbation may be partly through the inappropriate activation of antigen-presenting cells including DC.

Lung deposition of multi-walledcarbon nanotubes (MWCNT) induces pulmonary toxicity. Commercial MWCNT vary greatly in physicochemical properties and consequently in biological effects. To identify determinants of MWCNT-induced toxicity, we analyzed the effects of pulmonary exposure to 10 commercial MWCNT (supplied in three groups of different dimensions, with one pristine and two/three surface modified in each group). We characterized morphology, chemical composition, surface area and functionalization levels. MWCNT were deposited in lungs of female C57BL/6J mice by intratracheal instillation of 0, 6, 18 or 54 μg/mouse. Pulmonary inflammation (neutrophil influx in bronchoalveolar lavage (BAL)) and genotoxicity were determined on day 1, 28 or 92. Histopathology of the lungs was performed on day 28 and 92. All MWCNT induced similar histological changes. Lymphocytic aggregates were detected for all MWCNT on day 28 and 92. Using adjusted, multiple regression analyses, inflammation and genotoxicity were related to dose, time and physicochemical properties. The specific surface area (BET) was identified as a positive predictor of pulmonary inflammation on all post-exposure days. In addition, length significantly predicted pulmonary inflammation, whereas surface oxidation (-OH and -COOH) was predictor of lowered inflammation on day 28. BET surface area, and therefore diameter, significantly predicted genotoxicity in BAL fluid cells and lung tissue such that lower BET surface area or correspondingly larger diameter was associated with increased genotoxicity. This study provides information on possible toxicity-driving physicochemical properties of MWCNT. The results may contribute to safe-by-design manufacturing of MWCNT, thereby minimizing adverse effects. PMID:27323647

Endotoxin is often used to activate NF-κB in vitro when assessing NLRP3 inflammasome activation by various exogenous particles including nanoparticles. However, the endogenous source of this signal 1 is unknown. High-mobility group box 1 (HMGB1) is known to play a critical role in acute lung injury, however the potential contribution of the alarmin HMGB1 to NLRP3 Inflammasome activation has not been determined in response to nanoparticles in vivo. In this study, the ability of multi-walledcarbon nanotubes (MWCNT) to cause release of HMGB1 in vitro and in vivo, as well as the potential of HMGB1 to function as signal 1 in vitro and in vivo, was determined. HMGB1 activity in vivo was assessed by administration of HMGB1 neutralization antibodies following MWCNT exposure. Caspase-1−/− mice were utilized to elucidate the dependence of HMGB1 secretion on NLRP3 inflammasome activity. MWCNT exposure increased extracellular HMGB1 levels in primary alveolar macrophages from C57Bl/6 mice and C10 mouse epithelial cell culture supernatants, and in C57Bl/6 mouse lung lavage fluid. MWCNT-induced HMGB1 secretion was dependent upon caspase-1. HMGB1 increased MWCNT-induced IL-1β release from macrophages in vitro, and neutralization of extracellular HMGB1 reduced MWCNT-induced IL-1β secretion in vivo. HMGB1 neutralization was accompanied with overall decreased inflammation. In summary, this study suggests extracellular HMGB1 participates in NLRP3 inflammasome activity and regulates IL-1β associated sterile inflammation induced by MWCNT. PMID:24983895

Multi-walledcarbon nanotube-hydroxyapatite composites (MWCNT-HAP) were employed as the sorbent to study the sorption characteristic of Pb (II) using batch experiments. Effects of dosage of adsorbent, pH, ionic strength, contact time, initial concentration of lead and temperature were investigated. The results indicated that the removal of lead to MWCNT-HAP composites was strongly dependent on dosage of adsorbent, pH, temperature, and independent of ionic strength. The maximum adsorption capacity of lead was about 716. 13 mg.g-1 at 20°C, with a solid/liquid ratio of 0.08 g.L-1, pH0 = 5.5 and an initial concentration of 100 mg.L-1. The adsorption of Pb(II) on MWCNT-HAP composites was a fast process and could reach the equilibrium within 60 minutes. Ninety percent of the maximum adsorption capacity could be reached in 30 minutes. The kinetic data were fitted to pseudo-second-order kinetic model reasonably well. The kinetic sorption of Pb(II) on MWCNT-HAP was well described by pseudo-second-order kinetic model. The negative free energy calculated from the temperature dependent sorption isotherms suggested that the sorption of Pb(II) on MWCNT-HAP composites was a spontaneous process, and high temperature favored the adsorption process. The higher correlation coefficient values (R2 = 0. 999 8 - 1. 000 0) of Langmuir isotherm model at different temperatures suggested that Langmuir model could be used to simulate the sorption of Pb(II) on MWCNT-HAP. The adsorption mechanism mainly involves surface complexation between the lead ions and the surface oxygen-containing functional groups of the MWCNT-HAP, dissolution of HAP and precipitation of pyromorphite [Pb10 (PO4)6 (OH) 2], ion exchange reaction between Pb2+ and Ca2+ of hydroxyapatite. PMID:26489325

Available on the Internet, the CORAL software (http://www.insilico.eu/coral) has been used to build up quasi-quantitative structure-activity relationships (quasi-QSAR) for prediction of mutagenic potential of multi-walledcarbon-nanotubes (MWCNTs). In contrast with the previous models built up by CORAL which were based on representation of the molecular structure by simplified molecular input-line entry system (SMILES) the quasi-QSARs based on the representation of conditions (not on the molecular structure) such as concentration, presence (absence) S9 mix, the using (or without the using) of preincubation were encoded by so-called quasi-SMILES. The statistical characteristics of these models (quasi-QSARs) for three random splits into the visible training set and test set and invisible validation set are the following: (i) split 1: n=13, r(2)=0.8037, q(2)=0.7260, s=0.033, F=45 (training set); n=5, r(2)=0.9102, s=0.071 (test set); n=6, r(2)=0.7627, s=0.044 (validation set); (ii) split 2: n=13, r(2)=0.6446, q(2)=0.4733, s=0.045, F=20 (training set); n=5, r(2)=0.6785, s=0.054 (test set); n=6, r(2)=0.9593, s=0.032 (validation set); and (iii) n=14, r(2)=0.8087, q(2)=0.6975, s=0.026, F=51 (training set); n=5, r(2)=0.9453, s=0.074 (test set); n=5, r(2)=0.8951, s=0.052 (validation set). PMID:25465947

Background The incidence of papillary thyroid carcinoma (PTC) has risen steadily over the past few decades as well as the recurrence rates. It has been proposed that targeted ablative physical therapy could be a therapeutic modality in thyroid cancer. Targeted bio-affinity functionalized multi-walledcarbon nanotubes (BioNanofluid) act locally, to efficiently convert external light energy to heat thereby specifically killing cancer cells. This may represent a promising new cancer therapeutic modality, advancing beyond conventional laser ablation and other nanoparticle approaches. Methods Thyroid Stimulating Hormone Receptor (TSHR) was selected as a target for PTC cells, due to its wide expression. Either TSHR antibodies or Thyrogen or purified TSH (Thyrotropin) were chemically conjugated to our functionalized Bionanofluid. A diode laser system (532 nm) was used to illuminate a PTC cell line for set exposure times. Cell death was assessed using Trypan Blue staining. Results TSHR-targeted BioNanofluids were capable of selectively ablating BCPAP, a TSHR-positive PTC cell line, while not TSHR-null NSC-34 cells. We determined that a 2:1 BCPAP cell:α-TSHR-BioNanofluid conjugate ratio and a 30 second laser exposure killed approximately 60% of the BCPAP cells, while 65% and >70% of cells were ablated using Thyrotropin- and Thyrogen-BioNanofluid conjugates, respectively. Furthermore, minimal non-targeted killing was observed using selective controls. Conclusion A BioNanofluid platform offering a potential therapeutic path for papillary thyroid cancer has been investigated, with our in vitro results suggesting the development of a potent and rapid method of selective cancer cell killing. Therefore, BioNanofluid treatment emphasizes the need for new technology to treat patients with local recurrence and metastatic disease who are currently undergoing either re-operative neck explorations, repeated administration of radioactive iodine and as a last resort external beam

In this work, technetium-99 (99mTc) was used as the radiolabeling isotope to study the biodistribution of oxidized multi-walledcarbon nanotubes (oMWCNTs) and/or nanodiamonds (NDs) in mice after intravenous administration. The histological impact of non-radiolabeled oMWCNTs or NDs was investigated in comparison to the co-exposure groups. 99mTc-labeled nanomaterials had high stability in vivo and fast clearance from blood. After a single injection of oMWCNTs, the highest distribution was found in the lungs, with lower uptake in the liver/spleen. As for NDs injected alone, high distribution in the liver, spleen, and lungs was observed right after. However, uptake in the lungs was decreased obviously after 24 h, while high accumulation in the liver or spleen continued. After co-injection of oMWCNTs and NDs, oMWCNTs significantly affected the distribution pattern of NDs in vivo. Meanwhile, the increasing dose of oMWCNTs decreased the hepatic and splenic accumulation of NDs and gradually increased lung retention. On the contrary, the NDs had no significant effects on the distribution of oMWCNTs in mice. Histological photographs showed that oMWCNTs were mainly captured by lung macrophages, and NDs were located in the bronchi and alveoli after co-administration. oMWCNTs and NDs had different modes of micro-cells. In conclusion, the behavior and fate of NDs in mice depended strongly on oMWCNTs, but NDs had a small influence on the biodistribution and excretion pattern of oMWCNTs. PMID:22913534

The increased production and use of multi-walledcarbon nanotubes (MWCNTs) in a diverse array of consumer, medical, and industrial applications have raised concerns about potential human exposure to these materials in the workplace and ambient environments. Inhalation is a primary route of exposure to MWCNTs, and the existing data indicate that they are potentially hazardous to human health. While a 90-day rodent inhalation test (e.g., OECD Test No. 413: subchronic inhalation toxicity: 90-day study or EPA Health Effects Test Guidelines OPPTS 870.3465 90-day inhalation toxicity) is recommended by the U.S. Environmental Protection Agency Office of Pollution Prevention and Toxics for MWCNTs (and other CNTs) if they are to be commercially produced (Godwin et al. in ACS Nano 9:3409-3417, 2015), this test is time and cost-intensive and subject to scientific and ethical concerns. As a result, there has been much interest in transitioning away from studies on animals and moving toward human-based in vitro and in silico models. However, given the multiple mechanisms of toxicity associated with subchronic exposure to inhaled MWCNTs, a battery of non-animal tests will likely be needed to evaluate the key endpoints assessed by the 90-day rodent study. Pulmonary fibrosis is an important adverse outcome related to inhalation exposure to MWCNTs and one that the non-animal approach should be able to assess. This review summarizes the state-of-the-science regarding in vivo and in vitro toxicological methods for predicting MWCNT-induced pulmonary fibrosis. PMID:27215431

Some multi-walledcarbon nanotubes (MWCNTs) induce mesothelioma in rodents, straight MWCNTs showing a more pronounced effect than tangled MWCNTs. As primary and secondary genotoxicity may play a role in MWCNT carcinogenesis, we used a battery of assays for DNA damage and micronuclei to compare the genotoxicity of straight (MWCNT-S) and tangled MWCNTs (MWCNT-T) in vitro (primary genotoxicity) and in vivo (primary or secondary genotoxicity). C57Bl/6 mice showed a dose-dependent increase in DNA strand breaks, as measured by the comet assay, in lung cells 24 h after a single pharyngeal aspiration of MWCNT-S (1-200 μg/mouse). An increase was also observed for DNA strand breaks in lung and bronchoalveolar lavage (BAL) cells and for micronucleated alveolar type II cells in mice exposed to aerosolized MWCNT-S (8.2-10.8 mg/m(3)) for 4 d, 4 h/d. No systemic genotoxic effects, assessed by the γ-H2AX assay in blood mononuclear leukocytes or by micronucleated polychromatic erythrocytes (MNPCEs) in bone marrow or blood, were observed for MWCNT-S by either exposure technique. MWCNT-T showed a dose-related decrease in DNA damage in BAL and lung cells of mice after a single pharyngeal aspiration (1-200 μg/mouse) and in MNPCEs after inhalation exposure (17.5 mg/m(3)). In vitro in human bronchial epithelial BEAS-2B cells, MWCNT-S induced DNA strand breaks at low doses (5 and 10 μg/cm(2)), while MWCNT-T increased strand breakage only at 200 μg/cm(2). Neither of the MWCNTs was able to induce micronuclei in vitro. Our findings suggest that both primary and secondary mechanisms may be involved in the genotoxicity of straight MWCNTs. PMID:26674712

Carbon nanotubes (CNT) are cytotoxic to several cell types. However, the mechanism of CNT toxicity has not been fully studied, and dosimetric analyses of CNT in the cell culture system are lacking. Here, we describe a novel, high throughput method to measure cellular uptake of CNT using turbimetry. BEAS-2B, a human bronchial epithelial cell line, was used to investigate cellular uptake, cytotoxicity, and inflammatory effects of multi-walled CNT (MWCNT). The cytotoxicity of MWCNT was higher than that of crocidolite asbestos in BEAS-2B cells. The IC{sub 50} of MWCNT was 12 {mu}g/ml, whereas that of asbestos (crocidolite) was 678 {mu}g/ml. Over the course of 5 to 8 h, BEAS-2B cells took up 17-18% of the MWCNT when they were added to the culture medium at a concentration of 10 {mu}g/ml. BEAS-2B cells were exposed to 2, 5, or 10 {mu}g/ml of MWCNT, and total RNA was extracted for cytokine cDNA primer array assays. The culture supernatant was collected for cytokine antibody array assays. Cytokines IL-6 and IL-8 increased in a dose dependent manner at both the mRNA and protein levels. Migration inhibitory factor (MIF) also increased in the culture supernatant in response to MWCNT. A phosphokinase array study using lysates from BEAS-2B cells exposed to MWCNT indicated that phosphorylation of p38, ERK1, and HSP27 increased significantly in response to MWCNT. Results from a reporter gene assays using the NF-{kappa}B or AP-1 promoter linked to the luciferase gene in transiently transfected CHO-KI cells revealed that NF-{kappa}B was activated following MWCNT exposure, while AP-1 was not changed. Collectively, MWCNT activated NF-{kappa}B, enhanced phosphorylation of MAP kinase pathway components, and increased production of proinflammatory cytokines in human bronchial epithelial cells.

Carbon nanotubes (CNTs) are emerging nanotechnology materials which are likely to be mass-produced in the near future. However, prior to mass-production, certain health-related concerns should first be addressed. For example, when inhaled, the thin-fibrous shape and the biopersistent characteristics of CNTs may cause pulmonary diseases, in a manner similar to asbestos. In the present study, mouse macrophages (J774.1) were exposed to highly-purified multi-walled CNTs (MWCNTs, 67 nm) or to UICC crocidolite in order to evaluate the toxicity of these nano-size fibers. The cytotoxicity of MWCNTs was found to be higher than that of crocidolite. The toxic effect of MWCNTs was not affected by N-acetylcysteine, an antioxidant, or buthionine sulfoximine, a glutathione synthesis inhibitor. cDNA microarray analyses suggested that the cytotoxicity of MWCNTs could not be explained satisfactorily by either an increase or decrease of gene expression, although mRNA levels of some cytokines were slightly increased by MWCNTs. Moreover, MWCNTs did not significantly activate either MAP kinases such as ERK, JNK and p38, nor common apoptosis pathways such as caspase 3 and PARP. Electron microscopic studies indicated that MWCNTs associate with the plasma membrane of macrophages and disrupt the integrity of the membrane. Several proteins were found to adsorb onto MWCNTs when MWCNT-exposed macrophages were gently lysed. One of these proteins was macrophage receptor with collagenous structure (MARCO). MARCO-transfected CHO-K1 cells associated with MWCNTs more rapidly than mock-transfected cells. These results indicate that MWCNTs probably trigger cytotoxic effects in phagocytotic cells by reacting with MARCO on the plasma membrane and rupturing the plasma membrane.

The kinetics of adsorption and parameters of equilibrium adsorption of Methylene Blue (MB) on hybrid laponite-multi-walledcarbon nanotube (NT) particles in aqueous suspensions were determined. The laponite platelets were used in order to facilitate disaggregation of NTs in aqueous suspensions and enhance the adsorption capacity of hybrid particles for MB. Experiments were performed at room temperature (298K), and the laponite/NT ratio (Xl) was varied in the range of 0-0.5. For elucidation of the mechanism of MB adsorption on hybrid particles, the electrical conductivity of the system as well as the electrokinetic potential of laponite-NT hybrid particles were measured. Three different stages in the kinetics of adsorption of MB on the surface of NTs or hybrid laponite-NT particles were discovered to be a fast initial stage I (adsorption time t=0-10min), a slower intermediate stage II (up to t=120min) and a long-lasting final stage III (up to t=24hr). The presence of these stages was explained accounting for different types of interactions between MB and adsorbent particles, as well as for the changes in the structure of aggregates of NT particles and the long-range processes of restructuring of laponite platelets on the surface of NTs. The analysis of experimental data on specific surface area versus the value of Xl evidenced in favor of the model with linear contacts between rigid laponite platelets and NTs. It was also concluded that electrostatic interactions control the first stage of adsorption at low MB concentrations. PMID:27090704

Multiwallcarbon nanotubes (MWCNTs) and diamond are renowned as superlative material due to their relatively high thermal conductivity and hardness while comparing with any bulk materials. In this research, polyacrylonitrile (PAN) solution incorporated with MWCNTs at an alteration of mass fractions (0 wt%, 0.6 wt%, 1 wt%, 2 wt%) were fabricated via electrospinning under optimized parameters. Dried composite nanofibers were stabilized and carbonized, after which water base polytrafluorethylene (PTFE) mixed with nano diamond powder solution was spin coated on them. Scanning electron microscopy, Raman spectroscopy, X-ray scattering and Laserflash thermal conductivity were used to characterize the composite nanofiber sheets. The result shows that the thermal conductivity increased to 4.825 W/m K from 2.061 W/mK. The improvement of thermal conductivities is suggesting the incorporation of MWCNTs. PMID:27433684

Carbon nanotubes (CNTs) are a novel nanomaterial with wide potential applications; however the adverse effects of CNTs following environmental exposure have recently received significant attention. Herein, we explore the systemic toxicity and potential influence of 0-1000 mg L(-1) the multi-walled CNTs on red spinach. The multi-walled CNTs exposed plants exhibited growth inhibition and cell death after 15 days of hydroponic culture. The multi-walled CNTs had adverse effects on root and leaf morphology, as observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Raman spectroscopy detected the multi-walled CNTs in leaves. Biomarkers of nanoparticle toxicity, reactive oxygen species (ROS), and cell damage in the red spinach were greatly increased 15 days post-exposure to the multi-walled CNTs. These effects were reversed when the multi-walled CNTs were supplemented with ascorbic acid (AsA), suggesting a role of ROS in the multi-walled CNT-induced toxicity and that the primary mechanism of the multi-walled CNTs' toxicity is oxidative stress. PMID:23146354

In this work, NACE with UV detection is combined with SPE using multi-walledcarbon nanotubes (MWCNT) as stationary phase to determine a group of seven pesticides (pirimicarb, pyrifenox, penconazol, carbendazim, cyromazine, pyrimethanil and cyprodinil) in mineral water samples using ametryn as internal standard. The optimized BGE, consisting of a mixture of MeOH and ACN (1:2 v/v) with 90 mM SDS and 20.5 mM HClO(4), was satisfactory to get a good resolution of the seven compounds in less than 13 min. On-line preconcentration was carried out by electrokinetic injection of the sample dissolved in 78:22 v/v MeOH/ACN, 1.11 mM HClO(4). Repeatability was studied for the same day (n=4), for nine different days (n=36) and for four different capillaries. RSD values were appropriate in all cases, i.e. in the range 4.3-9.4% between different capillaries. MWCNT of 10-15 nm od, 2-6 nm id and 0.1-10 mum length were used as SPE materials for the preconcentration of these pesticides from water samples. SPE parameters influencing the enrichment were optimized and the most favorable conditions were as follows: the amount of stationary phase, eluent, sample pH and sample volume were 40 mg MWCNT, 10 mL ACN and 10 mL dichloromethane containing 5% v/v formic acid, pH 8.0, and 750 mL, respectively. Mean recovery values ranged between 53 and 94% for Milli-Q water and between 47 and 93% for mineral waters (RSD values were in the range 2-16%). The method allowed the determination of these pesticides at concentrations below the maximum residue limits established by the European Union legislation (LOD in the range 27-58 ng/L). When the cost, amount and type of the carbon nanotubes used in this work are compared with those carbon nanotubes previously used in the literature it is clear that the proposed materials can be used as economical stationary phases, even cheaper than conventional SPE cartridges. PMID:18956435

Owing to their unique structure and excellent electrical property, carbon nanotubes (CNTs) as an ideal candidate for making future electronic components have great application potentiality. In order to meet the requirements for space application in electronic components, it is necessary to study structural changes and damage mechanisms of multi-walledcarbon nanotubes (MWCNTs), caused by the irradiations of 70 and 110 keV electrons. In the paper, the changes of structure and damage mechanisms in the irradiated MWCNTs, induced by the irradiations of 70 and 110 keV electrons, are investigated. The changes in surface morphology and structure of the irradiated MWCNT film are characterized using scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS), Raman spectroscopy, x-ray diffraction analysis (XRD), and electron paramagnetic resonance (EPR) spectroscopy. It is found that the MWCNTs show different behaviors in structural changes after 70 and 110 keV electron irradiation due to different damage mechanisms. SEM results reveal that the irradiation of 70 keV electrons does not change surface morphology of the MWCNT film, while the irradiation of 110 keV electrons with a high fluence of 5 × 1015 cm-2 leads to evident morphological changes, such as the formation of a rough surface, the entanglement of nanotubes and the shrinkage of nanotubes. Based on Raman spectroscopy, XPS, and XRD analyses, it is confirmed that the irradiation of 70 keV electrons increases the interlayer spacing of the MWCNTs and disorders their structure through electronic excitations and ionization effects, while the irradiation of 110 keV electrons obviously reduces the interlayer spacing of the MWCNTs and improves their graphitic order through knock-on atom displacements. The improvement of the irradiated MWCNTs by 110 keV electrons is attributed to the restructuring of defect sites induced by knock-on atom displacements. EPR spectroscopic analyses reveal that the MWCNTs exposed

The poor dispersion in aqueous solution limited the application of carbon nanotubes (CNTs) in biological field. Here we used DCC/DMAP as Catalysis to prepare lysine modified multi-walledcarbon nanotubes (MWNTs). FT-IR and TGA demonstrated that lysine have been successfully grafted to MWNTs, EA showed that lysine graft rate up to 23.4%. The dispersion of lysine modified MWNTs was investigated by direct visual inspection and microscope observation, the result showed that lysine modified MWNTs can be dispersed in aqueous solution and keep stable for long time.

The electronic structure of individual multi-walledcarbon nanotubes (MWCNTs) has been probed using scanning transmission X-ray microscopy (STXM). Although transmission electron microscope (TEM) images show that the exterior of the MWCNTs are clean and straight; the inside structure of some of the MWCNTs is much less well ordered, as revealed by STXM. The amorphization of the interior tubes can be introduced in the growth or modification processes. Moreover, TEM measurement with high dose may also lead to the inside damage. Our results reveal that the structure of individual MWCNTs can be complex and suggest that electronic structure measurements are an important tool for characterizing carbon nanomaterials.

This paper studies the effect of carbon nanotubes on laser cutting of injection molded multi-walledcarbon nanotubes/poly methyl methacrylate (MWCNT/PMMA) composite. Also the effect of processing parameters on laser cutting of MWCNT/PMMA nanocomposites is investigated in this study. Design of experiments is performed using full factorial method. Variable input factors are considered as MWCNT wt% in four levels, laser power in three levels and feed rate in three levels. Output parameters of this study are heat affected zone (HAZ), the average kerf width, and the taper kerf of the samples. Continuous wave CO2 laser is used in the cutting process of the samples. Output parameters are studied in direction perpendicular to the flow direction. Experiments analysis is performed using analysis of variance method. Regarding the HAZ, results show that the most effective parameters are feed rate and the amount of the carbon nanotubes. High available carbon nanotube percentage causes approximately 50% decrease in the HAZ. Findings also clearly show that average kerf width is influenced by the three variable input factors. The tapering kerf of the samples is also significantly depended on the percentage of the carbon nanotube.

We report for the first time the use of polyhistidine (Polyhis) to efficiently disperse multiwall carbon nanotubes (MWCNTs). The optimum dispersion MWCNT-Polyhis was obtained by sonicating for 30 min 1.0 mg mL(-1) MWCNTs in 0.25 mg mL(-1) Polyhis solution prepared in 75:25 (v/v) ethanol/0.200 M acetate buffer solution pH 5.00. The dispersion was characterized by scanning electron microscopy, and by cyclic voltammetry and amperometry using ascorbic acid as redox marker. The modification of glassy carbon electrodes with MWCNT-Polyhis produces a drastic decrease in the overvoltage for the oxidation of ascorbic acid (580 mV) at variance with the response observed at glassy carbon electrodes modified just with Polyhis, where the charge transfer is more difficult due to the blocking effect of the polymer. The reproducibility for the sensitivities obtained after 10 successive calibration plots using the same surface was 6.3%. The MWCNT-modified glassy carbon electrode demonstrated to be highly stable since after 45 days storage at room temperature the response was 94.0% of the original. The glassy carbon electrode modified with MWCNT-Polyhis dispersion was successfully used to quantify dopamine or uric acid at nanomolar levels, even in the presence of large excess of ascorbic acid. Determinations of uric acid in human blood serum samples demonstrated a very good correlation with the value reported by Wienner laboratory. PMID:22123112

Field emission from closed and open-ended multi-walled nanotubes (MWNTs) was studied by field-emission microscopy. As an application of nanotube field emitters, we manufactured lighting elements with the structure of a triode-type vacuum tube by replacing the conventional thermionic cathodes with the MWNT field emitters. Stable electron emission, adequate luminance and long life of the tubes have been demonstrated.

Background Engineered carbon nanotubes are currently used in many consumer and industrial products such as paints, sunscreens, cosmetics, toiletries, electronic processes and industrial lubricants. Carbon nanotubes are among the more widely used nanoparticles and come in two major commercial forms, single-walled carbon nanotubes (SWCNT) and the more rigid, multi-walledcarbon nanotubes (MWCNT). The low density and small size of these particles makes respiratory exposures likely. Many of the potential health hazards have not been investigated, including their potential for carcinogenicity. We, therefore, utilized a two stage initiation/promotion protocol to determine whether inhaled MWCNT act as a complete carcinogen and/or promote the growth of cells with existing DNA damage. Six week old, male, B6C3F1 mice received a single intraperitoneal (ip) injection of either the initiator methylcholanthrene(MCA, 10 μg/g BW, i.p.), or vehicle (corn oil). One week after i.p. injections, mice were exposed by inhalation to MWCNT (5 mg/m3, 5 hours/day, 5 days/week) or filtered air (controls) for a total of 15 days. At 17 months post-exposure, mice were euthanized and examined for lung tumor formation. Results Twenty-three percent of the filtered air controls, 26.5% of the MWCNT-exposed, and 51.9% of the MCA-exposed mice, had lung bronchiolo-alveolar adenomas and lung adenocarcinomas. The average number of tumors per mouse was 0.25, 0.81 and 0.38 respectively. By contrast, 90.5% of the mice which received MCA followed by MWCNT had bronchiolo-alveolar adenomas and adenocarcinomas with an average of 2.9 tumors per mouse 17months after exposure. Indeed, 62% of the mice exposed to MCA followed by MWCNT had bronchiolo-alveolar adenocarcinomas compared to 13% of the mice that received filtered air, 22% of the MCA-exposed, or 14% of the MWCNT-exposed. Mice with early morbidity resulting in euthanasia had the highest rate of metastatic disease. Three mice exposed to both MCA and

Carbon nanotubes (CNTs) have often been used as additives to improve the properties of refractories containing carbon. However, it is very difficult to evenly distribute CNTs in the matrix. In order to solve this difficulty, an alumina/multi-walledcarbon nanotube (MWCNT) (AM) composite powder in which MWCNTs had grown on the surfaces of Al2O3 particles was developed and used in alumina-carbon (Al2O3-C) refractories. The effects of the AM composite powders on the microstructure and properties of the Al2O3-C refractories were studied and compared with the commercial MWCNTs. The nanocomposite powders significantly improved the distribution uniformity of MWCNTs in the Al2O3-C matrix. The densification, fracture properties, thermal shock resistance, and slag corrosion resistance were enhanced due to the well-dispersed MWCNTs. On the contrary, no improvement of the densification, fracture properties, and thermal shock resistance of the refractories was achieved by addition of commercial MWCNTs due to the agglomeration of MWCNTs.

Pd and PdSn (Pd:Sn atomic ratios of 90:10), supported on MultiWallCarbon Nanotubes (MWCNT) or Carbon (C), are prepared by an electron beam irradiation reduction method. The obtained materials are characterized by X-Ray diffraction (XRD), Energy dispersive X-ray analysis (EDX), Transmission electron Microscopy (TEM) and Cyclic Voltammetry (CV). The activity for ethanol electro-oxidation is tested in alkaline medium, at room temperature, using Cyclic Voltammetry and Chronoamperometry (CA) and in a single alkaline direct ethanol fuel cell (ADEFC), in the temperature range of 60-90 °C. CV analysis finds that Pd/MWCNT and PdSn/MWCNT presents onset potentials changing to negative values and high current values, compared to Pd/C and PdSn/C electrocatalysts. ATR-FTIR analysis, performed during the CV, identifies acetate and acetaldehyde as principal products formed during the ethanol electro-oxidation, with low conversion to CO2. In single fuel cell tests, at 85 °C, using 2.0 mol L-1 ethanol in 2.0 mol L-1 KOH solutions, the electrocatalysts supported on MWCNT, also, show higher power densities, compared to the materials supported on carbon: PdSn/MWCNT, presents the best result (36 mW cm-2). The results show that the use of MWCNT, instead of carbon, as support, plus the addition of small amounts of Sn to Pd, improves the electrocatalytic activity for Ethanol Oxidation Reaction (EOR).

Aim: The aim of this study was to design multi-walledcarbon nanotubes (MWCNTs) loaded with paclitaxel (PTX) anti-cancer drug and investigate its anti-cancerous efficacy of human gastric cancer. Background: Carbon nanotubes (CNTs) represent a novel nano-materials applied in various fields such as drug delivery due to their unique chemical properties and high drug loading. Patients and methods: In this study, multi-walledcarbon nanotubes (MWCNTs) pre-functionalized covalently with a paclitaxel (PTX) as an anti-cancer drug and evaluated by different analyses including, scanning electron microscope (SEM), particle size analyzer and cellular analyses. Results: A well conjugated of anti-cancer drug on the carbon nanotube surfaces was shown. This study demonstrates that the MWCN-PTX complex is a potentially useful system for delivery of anti-cancer drugs. The flow cytometry, CFU and MTT assay results have disclosed that MWCNT/PTXs might promote apoptosis in MKN-45 gastric adenocarcinoma cell line. Conclusion: According to results, our simple method can be designed a candidate material for chemotherapy. It has presented a few bio-related applications including, their successful use as a nano-carriers for drug transport. PMID:27458512

A novel and sensitive electrochemical DNA biosensor based on multi-walledcarbon nanotubes functionalized with a thio group (MWNTs-SH) and gold nanoparticles (GNPs) for covalent DNA immobilization and enhanced hybridization detection is described. The key step for developing this novel DNA biosensor is to cut the pristine MWNT into short and generate lots of active sites simultaneously. With this approach, the target DNA could be quantified in a linear range from 8.5×10-10 to 1.5×10-5 mol/L, with a detection limit of 1.67×10-11 mol/L by 3σ.

Porous carbon is the most widely used electrode materials in energy storage devices. It is generally accepted that in such electrodes, mesoporosity is more desired in supercapacitor than microporosity for the ions tranportation. However, the relatively poor conductivity of porous carbon often leads to low capacitance. To improve the capacity of mesoporous carbon based electrode, we designed a composite film composed of mesoporous carbon, multiwalled carbon nanotubes (MWNTs) and conducting polymer, Poly-3,4-ethylenedioxythiophene/poly(styrenesulfonate) (PEDOT-PSS), and hoped that each component in the composed film could contribute synergetically to improve electrochemical properties. The electrochemical performance of the film was evaluated by cyclic voltammetry and constant current charge/discharge method. With the assistance of MWNTs and conducting polymer, the specific capacitance of the mesoporous carbon based electrode was amplified six times. The electrode also presented excellent charge/discharge rate and good cycling stability, retaining about 94% of its initial capacitance after 1000 cycles. The results demonstrated that mesoporous carbon is more effectively utilized with assistance of MWNTs and conducting polymer in the electrode. Such method is very promising for the future applications of the porous carbon in electrode materials for high performance electrochemical supercapacitors. PMID:25924364

BACKGROUND The lymphatic system plays a significant role in the defense of a subject against breast cancer and is one of the major pathways for the metastasis of breast cancer. To improve the prognosis, many means, including surgery, radiotherapy, and chemotherapy, have been used. However, the combination of all these modalities has limited efﬁcacy. Lymph nodes, therefore, have become an exceptionally potential target organ in cancer chemotherapy. MATERIAL AND METHODS A lymph node metastatic model of breast cancer was established in BALB/c mice. Magnetic multi-walledcarbon nanotube carrier with good adsorption and lymph node-targeting capacity was prepared and conjugated with doxorubicin to make the magnetic multi-walledcarbon nanotube-doxorubicin suspension. Dispersions of doxorubicin, magnetic multi-walledcarbon nanotube-doxorubicin, and magnetic multi-walledcarbon nanotube were injected into lymph node metastatic mice to compare their inhibitory effects on tumor cells in vivo. Inhibition of these dispersions on EMT-6 breast cancer cells was detected via MTT assay in vitro. RESULTS Although no significant difference was found between the effects of doxorubicin and magnetic multi-walledcarbon nanotube-doxorubicin with the same concentration of doxorubicin on EMT-6 breast cancer cells in vitro, in terms of sizes of metastatic lymph nodes and xenograft tumors, apoptosis in metastatic lymph nodes, and adverse reactions, the magnetic multi-walledcarbon nanotube-doxorubicin group differed significantly from the other groups. CONCLUSIONS The magnetic multi-walledcarbon nanotube-doxorubicin clearly played an inhibitory role in lymph node metastases to EMT-6 breast cancer cells. PMID:27385226

Background The lymphatic system plays a significant role in the defense of a subject against breast cancer and is one of the major pathways for the metastasis of breast cancer. To improve the prognosis, many means, including surgery, radiotherapy, and chemotherapy, have been used. However, the combination of all these modalities has limited efficacy. Lymph nodes, therefore, have become an exceptionally potential target organ in cancer chemotherapy. Material/Methods A lymph node metastatic model of breast cancer was established in BALB/c mice. Magnetic multi-walledcarbon nanotube carrier with good adsorption and lymph node-targeting capacity was prepared and conjugated with doxorubicin to make the magnetic multi-walledcarbon nanotube-doxorubicin suspension. Dispersions of doxorubicin, magnetic multi-walledcarbon nanotube-doxorubicin, and magnetic multi-walledcarbon nanotube were injected into lymph node metastatic mice to compare their inhibitory effects on tumor cells in vivo. Inhibition of these dispersions on EMT-6 breast cancer cells was detected via MTT assay in vitro. Results Although no significant difference was found between the effects of doxorubicin and magnetic multi-walledcarbon nanotube-doxorubicin with the same concentration of doxorubicin on EMT-6 breast cancer cells in vitro, in terms of sizes of metastatic lymph nodes and xenograft tumors, apoptosis in metastatic lymph nodes, and adverse reactions, the magnetic multi-walledcarbon nanotube-doxorubicin group differed significantly from the other groups. Conclusions The magnetic multi-walledcarbon nanotube-doxorubicin clearly played an inhibitory role in lymph node metastases to EMT-6 breast cancer cells. PMID:27385226

The synthesis and characterization of gas phase oxygen- and nitrogen-functionalized multi-walledcarbon nanotubes (OMWCNTs and NMWCNTs) and the dispersibility of these tubes in organic solvents were investigated. Recently, carbon nanotubes have shown supreme capacity to effectively enhance the efficiency of organic solar cells (OSCs). A critical challenge is to individualize tubes from their bundles in order to provide homogenous nano-domains in the active layer of OSCs. OMWCNTs and NMWCNTs were synthesized via HNO3 vapor and NH3 treatments, respectively. Surface functional groups and the structure of the tubes were analyzed by temperature-programmed desorption, Fourier transform infrared spectroscopy, transmission electron microscopy, and Raman spectroscopy which confirmed the formation of functional groups on the tube surface and the enhancement of surface defects. Elemental analysis demonstrated that the oxygen and nitrogen content increased with increasing treatment time of the multi-walledcarbon nanotube (MWCNT) in HNO3 vapor. According to ultra-violet visible spectroscopy, modification of the MWCNT increased the extinction coefficients of the tubes owing to enhanced compatibility of the functionalized tubes with organic matrices.

The synthesis and characterization of gas phase oxygen- and nitrogen-functionalized multi-walledcarbon nanotubes (OMWCNTs and NMWCNTs) and the dispersibility of these tubes in organic solvents were investigated. Recently, carbon nanotubes have shown supreme capacity to effectively enhance the efficiency of organic solar cells (OSCs). A critical challenge is to individualize tubes from their bundles in order to provide homogenous nano-domains in the active layer of OSCs. OMWCNTs and NMWCNTs were synthesized via HNO3 vapor and NH3 treatments, respectively. Surface functional groups and the structure of the tubes were analyzed by temperature-programmed desorption, Fourier transform infrared spectroscopy, transmission electron microscopy, and Raman spectroscopy which confirmed the formation of functional groups on the tube surface and the enhancement of surface defects. Elemental analysis demonstrated that the oxygen and nitrogen content increased with increasing treatment time of the multi-walledcarbon nanotube (MWCNT) in HNO3 vapor. According to ultra-violet visible spectroscopy, modification of the MWCNT increased the extinction coefficients of the tubes owing to enhanced compatibility of the functionalized tubes with organic matrices. PMID:27188622

The synthesis and characterization of gas phase oxygen- and nitrogen-functionalized multi-walledcarbon nanotubes (OMWCNTs and NMWCNTs) and the dispersibility of these tubes in organic solvents were investigated. Recently, carbon nanotubes have shown supreme capacity to effectively enhance the efficiency of organic solar cells (OSCs). A critical challenge is to individualize tubes from their bundles in order to provide homogenous nano-domains in the active layer of OSCs. OMWCNTs and NMWCNTs were synthesized via HNO3 vapor and NH3 treatments, respectively. Surface functional groups and the structure of the tubes were analyzed by temperature-programmed desorption, Fourier transform infrared spectroscopy, transmission electron microscopy, and Raman spectroscopy which confirmed the formation of functional groups on the tube surface and the enhancement of surface defects. Elemental analysis demonstrated that the oxygen and nitrogen content increased with increasing treatment time of the multi-walledcarbon nanotube (MWCNT) in HNO3 vapor. According to ultra-violet visible spectroscopy, modification of the MWCNT increased the extinction coefficients of the tubes owing to enhanced compatibility of the functionalized tubes with organic matrices. PMID:27188622

A novel sulfur-coated multi-walledcarbon nanotubes composite material (S-coated-MWCNTs) was prepared through capillarity between the sulfur and multi-walledcarbon nanotubes. The results of the TEM and XRD measurements reveal that S-coated-MWCNTs have a typical core-shell structure, and the MWCNTs serve as the cores and are dispersed individually into the sulfur matrices. The charge-discharge experiments of the lithium/sulfur cells demonstrated that the S-coated-MWCNTs cathode could maintain a reversible capacity of 670 mAh g -1 after 60 cycles, showing a greatly enhanced cycle ability as compared with the sulfur cathode with simple MWCNTs addition (S/MWCNTs) and the cathode using sulfur-coated carbon black composite (S-coated-CB). The EIS and SEM techniques were used to define and understand the impact of the microstructure of the composite electrode on its electrochemical performance. Derived from these studies, the main key factors to the improvement in the cycle life of the sulfur cathode were discussed.

Carbonaceous nanomaterials are being produced and integrated into consumer products and specialized applications at an accelerating rate. Recently, however, concerns have increased about the environmental, health and safety risks of these nanomaterials, particularly those chemically functionalized to enhance their aqueous colloidal stability and biocompatibility. In this dissertation research, I have investigated the role that surface-oxide concentration plays in the aqueous colloidal stability of multi-walledcarbon nanotubes (MWCNTs), a prominent class of engineered nanomaterials. To vary the concentration of surface oxides on the MWCNTs' surface, pristine (unmodified) tubes were treated with a wet-chemical oxidant (e.g., HNO3, H2SO4 /HNO3, KMnO4); the concentration of surface oxides imparted was measured by x-ray photoelectron spectroscopy (XPS). In conjunction with XPS, previously developed chemical derivatization techniques were used to determine the distribution of hydroxyl, carboxyl, and carbonyl functional groups present on the MWCNTs' surface. The length distribution and structural integrity of pristine and oxidized MWCNTs were characterized using atomic force microscopy and transmission electron microscopy, respectively. To examine the aqueous colloidal stability and aggregation properties of oxidized MWCNTs, sedimentation and time-resolved dynamic light scattering (TR-DLS) experiments were conducted on neat (i.e., ideal) suspensions prepared by prolonged sonication of MWCNTs in Milli-Q water. Over a range of environmentally relevant pH values (4--9) and electrolyte (NaCL, CaCl2) concentrations (0.001--1.000 M), the aggregation and colloidal properties of MWCNTs were found to agree with the basic tenants of DLVO theory, in that ( i) more highly oxidized, negatively charged MWCNTs remained stable over a wider range of solution conditions than lowly oxidized tubes, ( ii) oxidized MWCNTs adhered to the empirical Schulze-Hardy rule, and (iii) in early

Multi-walledcarbon nanotubes and powdered activated carbon were used as adsorbents for the successful removal of Reactive Red M-2BE textile dye from aqueous solutions. The adsorbents were characterised by infrared spectroscopy, N(2) adsorption/desorption isotherms and scanning electron microscopy. The effects of pH, shaking time and temperature on adsorption capacity were studied. In the acidic pH region (pH 2.0), the adsorption of the dye was favourable using both adsorbents. The contact time to obtain equilibrium at 298K was fixed at 1h for both adsorbents. The activation energy of the adsorption process was evaluated from 298 to 323K for both adsorbents. The Avrami fractional-order kinetic model provided the best fit to the experimental data compared with pseudo-first-order or pseudo-second-order kinetic adsorption models. For Reactive Red M-2BE dye, the equilibrium data were best fitted to the Liu isotherm model. Simulated dyehouse effluents were used to check the applicability of the proposed adsorbents for effluent treatment. PMID:21724329

We examined the biocompatibility and the safety of a-calcium sulfate hemihydrate (CSH)/multi-walledcarbon nanotube (MWCNT) composites for bone reconstruction application. The biocompatibility of the CSH/MWCNT composites was evaluated by the measures which taking L929 fibroblast cells cultured in the extracted liquid of the composite soaking solution and putting bone marrow stromal cells planted on the composite pellets in vitro, respectively. The cell proliferation was evaluated by MTT test and further observed using an inverted optical microscope and a scanning electric microscope. The toxicity of the composites was evaluated by acute and subacute systemic toxicity test. Long-term muscle and bone implantation in vivo tests were also conducted. L929 fibroblast cells grew well in the extracted liquid, as well as bone marrow stromal cells that could adhere on the surface of sample pellets and proliferated rapidly. MTT test showed that there were no significant differences between the experimental and control groups (P > 0.05). In vivo test manifested that the composites were no toxicity, no irritation to skin and good for bone defect reconstruction. It was proved that a-calcium sulfate hemihydrate (CSH)/multi-walledcarbon nanotube (MWCNT) composites exhibited excellent biocompatibility for the potential application in bone tissue engineering. PMID:22712392

Hydrogen storage into multi-walledcarbon nanotubes obtained by the decomposition of hydrocarbons using Ni-Li/SiO2 was investigated. The optimized reaction conditions for the synthesis of carbon nanotubes were 873K and W/F=40 g-cat.h/mol, and carbon nanotubes obtained by C2H6 decomposition were found to exhibit fairly large H2 storage capacity of 1 wt% at room temperature. The storage capacity increased with decreasing temperature and a capacity of 5 wt% was achieved at 77K, with 66% of adsorbed hydrogen being desorbable. Hydrogen adsorption by pi orbital in C-C bond coordination is proposed, observing both weakened Raman adsorption C-C peaks and the thermal release of CH4 after H2 storage. PMID:15509013

The thermal transport properties of multi-walledcarbon nanotubes (MWCNTs) were investigated by using non-equilibrium molecular dynamics simulation. The results show that the thermal conductivity of MWCNTs decreases significantly comparing to that of single-walled carbon nanotubes (SWCNTs) due to the inter-wall van der Waals interactions. The more interesting is a fact that the thermal conductance of MWCNTs is significantly greater than the thermal conductance summation of each SWCNTs. This is because the thermal conductance of a carbon nanotube protected by an outer tube is much larger than that of one that is not protected. Moreover, we also studied the thermal flux distribution of MWCNTs, and found that the outer tube plays a dominant role in heat energy transfer.

Surface modification of oxidized carbon nanotubes (O-CNTs) with silicon based anchoring groups (R-SiR3) is a relatively uncommon approach of the CNTs functionalization. Hydrosilane derivatives constitute an attractive subclass of compounds for silanization reactions on the CNTs surface. In this work, we report on the ZnCl2 catalytically controlled reaction (hydrosilane dehydrogenative cross-coupling, DHCC) of fluorinated hydrosilane probes with the carboxylic functions present on the surface of oxidized multi-wallcarbon nanotubes. Carbon nanotubes functionalized with essentially alcohol groups are also used to compare the selectivity of zinc chloride toward carboxylic groups. To assess the efficiency of functionalization, X-ray Photoelectron Spectroscopy is used to determine the qualitative and quantitative composition of the different samples. Solubility tests on the oxidized and silanized MWNTs are also carried out in the framework of the Hansen Solubility Parameters (HSP) theory to apprehend at another scale the effect of DHCC.

The fabrication of water-borne polyurethane nanocomposites containing multi-wall nanotubes has presented a significant technological challenge to those in the polymer community. Such conductive polyurethanes are of great interest to the paint and coatings industry for use in electrical grounding and shielding. Currently, these materials are formed by strong acidic reflux of the nanotubes and subsequent dispersal in the polymer matrix. This treatment can result in significant shortening of the tubes and degradation of the resulting mechanical and electrical transport properties. Here we present an alternate technique in which various conductive and non-conductive water-soluble polymers are physi-adsorbed to the surface of the nanotube. These interactions with the nanotubes result in highly uniform suspensions of water-based urethane coatings and bulk materials. We will examine the polymer chemistry and morphologies of these nanostructured materials and the resulting thermal, electrical and mechanical properties.

Multi-walledcarbon nanotube (MWCNT) reinforced copper (Cu) matrix composites, which exhibit chromium (Cr) carbide nanostructures at the MWCNT/Cu interface, were prepared through a carbide formation using CuCr alloy powder. The fully densified and oriented MWCNTs dispersed throughout the composites were prepared using spark plasma sintering (SPS) followed by hot extrusion. The tensile strengths of the MWCNT/CuCr composites increased with increasing MWCNTs content, while the tensile strength of MWCNT/Cu composite decreased from that of monolithic Cu. The enhanced tensile strength of the MWCNT/CuCr composites is a result of possible load-transfer mechanisms of the interfacial Cr carbide nanostructures. The multi-wall failure of MWCNTs observed in the fracture surface of the MWCNT/CuCr composites indicates an improvement in the load-bearing capacity of the MWCNTs. This result shows that the Cr carbide nanostructures effectively transferred the tensile load to the MWCNTs during fracture through carbide nanostructure formation in the MWCNT/Cu composite.

Multi-walledcarbon nanotube (MWCNT) reinforced copper (Cu) matrix composites, which exhibit chromium (Cr) carbide nanostructures at the MWCNT/Cu interface, were prepared through a carbide formation using CuCr alloy powder. The fully densified and oriented MWCNTs dispersed throughout the composites were prepared using spark plasma sintering (SPS) followed by hot extrusion. The tensile strengths of the MWCNT/CuCr composites increased with increasing MWCNTs content, while the tensile strength of MWCNT/Cu composite decreased from that of monolithic Cu. The enhanced tensile strength of the MWCNT/CuCr composites is a result of possible load-transfer mechanisms of the interfacial Cr carbide nanostructures. The multi-wall failure of MWCNTs observed in the fracture surface of the MWCNT/CuCr composites indicates an improvement in the load-bearing capacity of the MWCNTs. This result shows that the Cr carbide nanostructures effectively transferred the tensile load to the MWCNTs during fracture through carbide nanostructure formation in the MWCNT/Cu composite. PMID:22797555

A highly sensitive amperometric sulfadiazine sensor fabricated by electrochemical deposition of poly(cobalt tetraaminophthalocyanine) (poly(CoIITAPc)) on the surface of a multi-walledcarbon nanotubes-Nafion (MWCNTs-Nafion) modified electrode is described. This electrode showed a very attractive performance by combining the advantages of CoIITAPc, MWCNTs, and Nafion. Compared with the bare glassy carbon electrode (GCE) and the MWCNTs-Nafion modified electrode, the electrocatalytic activity of poly(CoIITAPc)-coated MWCNTs-Nafion GCE generated greatly improved electrochemical detections toward sulfadiazine including low oxidation potential, high current responses, and good anti-fouling performance. The oxidation peak currents of sulfadiazine obtained on the new modified electrode increased linearly while increasing the concentration of sulfadiazine from 0.5 to 43.5 μmol/L with the detection limit of 0.17 μmol/L. PMID:22661213

In situ scanning electron microscopy (SEM) observation of a tensile test was performed to investigate the fracturing behavior of multi-walledcarbon nanotubes (MWCNTs) in powder metallurgy Al matrix composites. A multiple peeling phenomenon during MWCNT fracturing was clearly observed. Its formation mechanism and resultant effect on the composite strength were examined. Through transition electron microscopy characterizations, it was observed that defective structures like inter-wall bridges cross-linked adjacent walls of MWCNTs. This structure was helpful to improve the inter-wall bonding conditions, leading to the effective load transfer between walls and resultant peeling behaviors of MWCNTs. These results might provide new understandings of the fracturing mechanisms of carbon nanotube reinforcements for designing high-performance nanocomposites. PMID:25437849

Comparative studies of optical transmission of single-walled carbon nanotubes (SWCNTs) and multi-walledcarbon nanotubes (MWCNTs), dispersed in nematic liquid crystal matrix 5CB, were carried out. The data evidence violations of Beer-Lambert-Bouguer (BLB) law both in cell thickness and concentration dependencies. The most striking is the fact that optical transmission dependencies for SWCNTs and MWCNTs were quite different in the nematic phase, but they were practically indistinguishable in the isotropic phase. Monte Carlo simulations of the impact of aggregation on direct transmission and violation of BLB law were also done. The results were discussed accounting for the tortuous shape of CNTs, their physical properties and aggregation, as well as strong impact of perturbations of the nematic 5CB structure inside coils and in the vicinity of CNT aggregates. PMID:25106504

The Raman spectra of the multi-walledcarbon nanotubes are studied with the laser power of 5-20 mW. We observe the Raman bands at ˜1352, 1581, 1607, and 2700 cm -1 with 5 mW laser power. As the laser power is increased to 10, 15 and 20 mW, the radial breathing modes (RBMs) of the single wall carbon nanotubes (SWNTs) appear in the range 200-610 cm -1. The diameter corresponding to the highest RBM is ˜0.37 nm, the lowest reported so far. The RBMs are attributed to the local synthesis of the SWNTs at the top surface of the samples at higher laser power.

Multi-walledcarbon nanotubes (CNTs) were directly used as a sustainable and green catalyst to convert ethanol into acetaldehyde in the presence of molecular oxygen. The C=O groups generated on the nanocarbon surface were demonstrated as active sites for the selective oxidation of ethanol to acetaldehyde. The transformation of disordered carbon debris on the CNT surface to ordered graphitic structures induced by thermal-treatment significantly enhanced the stability of the active C=O groups, and thus the catalytic performance. A high reactivity with approximately 60 % ethanol conversion and 93 % acetaldehyde selectivity was obtained over the optimized CNT catalyst at 270 °C. More importantly, the catalytic performance was quite stable even after 500 h, which is comparable with a supported gold catalyst. The robust catalytic performance displayed the potential application of CNTs in the industrial catalysis field. PMID:27282126

Fe filled carbon nanotubes were synthesized by atmospheric pressure chemical vapor deposition using a simple mixture of iron(III) acetylacetonate (Fe(acac){sub 3}) with a conventional photoresist and the effect of growth temperature (550-950 {sup o}C) on Fe filled nanotubes has been studied. Scanning electron microscopy results show that, as the growth temperature increases from 550 to 950 {sup o}C, the average diameter of the nanotubes increases while their number density decreases. High resolution transmission electron microscopy along with energy dispersive X-ray investigation shows that the nanotubes have a multi-walled structure with partial Fe filling for all growth temperatures. The graphitic nature of the nanotubes was observed via X-ray diffraction pattern. Raman analysis demonstrates that the degree of graphitization of the carbon nanotubes depends upon the growth temperature.

Background Prior studies have demonstrated a rapid and progressive acute phase response to bolus aspiration of multi-walledcarbon nanotubes (MWCNTs). In this study we sought to test the hypothesis that inhalation exposure to MWCNT produces a fibrotic response and that the response is chronically persistent. To address the hypothesis that inhaled MWCNTs cause persistent morphologic changes, male C57BL/6 J mice were exposed in a whole-body inhalation system to a MWCNT aerosol and the fibrotic response in the alveolar region examined at up to 336 days after termination of exposure. Methods Inhalation exposure was to a 5 mg/m3 MWCNT aerosol for 5 hours/day for 12 days (4 times/week for 3 weeks). At the end of inhalation exposures, lungs were either lavaged for analysis of bronchoalveolar lavage (BAL) or preserved by vascular perfusion of fixative while inflated with air at 1, 14, 84, 168 and 336 days post inhalation exposure. Separate, clean-air control groups were also studied. Light microscopy, enhanced darkfield microscopy and field emission electron microscopy (FESEM) of tissue sections were used to analyze the distribution of lung burden following inhalation exposure. Morphometric measurements of Sirius Red staining for fibrillar collagen were used to assess the connective tissue response. Serial section analysis of enhanced darkfield microscope images was used to examine the redistribution of MWCNT fibers within the lungs during the post-exposure period. Results At day 1 post-exposure 84 ± 3 and 16 ± 2 percent of the lung burden (Mean ± S.E., N = 5) were in the alveolar and airway regions, respectively. Initial distribution within the alveolar region was 56 ± 5, 7 ± 4 and 20 ± 3 percent of lung burden in alveolar macrophages, alveolar airspaces and alveolar tissue, respectively. Clearance reduced the alveolar macrophage burden of MWCNTs by 35 percent between 1 and 168 days post-exposure, while the content of MWCNTs in the

Polypyrrole multi-walledcarbon nanotube composite layers were used to modify the gold layer to measure heavy metal ions using the surface plasmon resonance technique. The new sensor was fabricated to detect trace amounts of mercury (Hg), lead (Pb), and iron (Fe) ions. In the present research, the sensitivity of a polypyrrole multi-walledcarbon nanotube composite layer and a polypyrrole layer were compared. The application of polypyrrole multi-walledcarbon nanotubes enhanced the sensitivity and accuracy of the sensor for detecting ions in an aqueous solution due to the binding of mercury, lead, and iron ions to the sensing layer. The Hg ion bonded to the sensing layer more strongly than did the Pb and Fe ions. The limitation of the sensor was calculated to be about 0.1 ppm, which produced an angle shift in the region of 0.3° to 0.6°. PMID:24733263

Polypyrrole multi-walledcarbon nanotube composite layers were used to modify the gold layer to measure heavy metal ions using the surface plasmon resonance technique. The new sensor was fabricated to detect trace amounts of mercury (Hg), lead (Pb), and iron (Fe) ions. In the present research, the sensitivity of a polypyrrole multi-walledcarbon nanotube composite layer and a polypyrrole layer were compared. The application of polypyrrole multi-walledcarbon nanotubes enhanced the sensitivity and accuracy of the sensor for detecting ions in an aqueous solution due to the binding of mercury, lead, and iron ions to the sensing layer. The Hg ion bonded to the sensing layer more strongly than did the Pb and Fe ions. The limitation of the sensor was calculated to be about 0.1 ppm, which produced an angle shift in the region of 0.3° to 0.6°. PMID:24733263

Release of Ni(1+) ions from NiTi alloy into tissue environment, biological response on the surface of NiTi and the allergic reaction of atopic people towards Ni are challengeable issues for biomedical application. In this study, composite coatings of hydroxyapatite-silicon multiwalledcarbon nano-tubes with 20wt% Silicon and 1wt% multiwalledcarbon nano-tubes of HA were deposited on a NiTi substrate using electrophoretic methods. The SEM images of coated samples exhibit a continuous and compact morphology for hydroxyapatite-silicon and hydroxyapatite-silicon-multiwalledcarbon nano-tubes coatings. Nano-indentation analysis on different locations of coatings represents the highest elastic modulus (45.8GPa) for HA-Si-MWCNTs which is between the elastic modulus of NiTi substrate (66.5GPa) and bone tissue (≈30GPa). This results in decrease of stress gradient on coating-substrate-bone interfaces during performance. The results of nano-scratch analysis show the highest critical distance of delamination (2.5mm) and normal load before failure (837mN) as well as highest critical contact pressure for hydroxyapatite-silicon-multiwalledcarbon nano-tubes coating. The cell culture results show that human mesenchymal stem cells are able to adhere and proliferate on the pure hydroxyapatite and composite coatings. The presence of both silicon and multiwalledcarbon nano-tubes (CS3) in the hydroxyapatite coating induce more adherence of viable human mesenchymal stem cells in contrast to the HA coated samples with only silicon (CS2). These results make hydroxyapatite-silicon-multiwalledcarbon nano-tubes a promising composite coating for future bone implant application. PMID:26897095

Multi-walledcarbon nanotubes (MWCNT) and powder activated carbon (PAC) were used as adsorbents for adsorption of Direct Blue 53 dye (DB-53) from aqueous solutions. The adsorbents were characterised using Raman spectroscopy, N2 adsorption/desorption isotherms, and scanning and transmission electron microscopy. The effects of initial pH, contact time and temperature on adsorption capacity of the adsorbents were investigated. At pH 2.0, optimum adsorption of the dye was achieved by both adsorbents. Equilibrium contact times of 3 and 4 h were achieved by MWCNT and PAC adsorbents, respectively. The general order kinetic model provided the best fit of the experimental data compared to pseudo-first order and pseudo-second order kinetic adsorption models. For DB-53 dye, the equilibrium data (298-323 K) were best fitted to the Sips isotherm model. The maximum sorption capacity for adsorption of the dye occurred at 323 K, with the values of 409.4 and 135.2 mg g(-1) for MWCNT and PAC, respectively. Studies of adsorption/desorption were conducted and the results showed that DB-53 loaded MWCNT could be regenerated (97.85%) using a mixture 50% acetone + 50% of 3 mol L(-1) NaOH. Simulated dye house effluents were used to evaluate the application of the adsorbents for effluent treatment (removal of 99.87% and 97.00% for MWCNT and PAC, respectively, were recorded). PMID:24076517

An amperometric sensor for the determination of epinephrine (EP) was fabricated by modifying the carbon paste electrode (CPE) with pristine multi-walledcarbon nanotubes (pMWCNTs) using bulk modification followed by drop casting of sodium dodecyl sulfate (SDS) onto the surface for its optimal potential application. The modified electrode showed an excellent electrocatalytic activity towards EP by decreasing the overpotential and greatly enhancing the current sensitivity. FE-SEM images confirmed the dispersion of pMWCNTs in the CPE matrix. EDX analysis ensured the surface coverage of SDS. A comparative study of pMWCNTs with those of oxidized MWCNTs (MWCNTsOX) modified electrodes reveals that the former is the best base material for the construction of the sensor with advantages of lower oxidation overpotential and the least background current. The performance of the modified electrode was impressive in terms of the least charge transfer resistance (Rct), highest values for diffusion coefficient (DEP) and standard heterogeneous electron transfer rate constant (k°). Analytical characterization of the modified electrode exhibited two linear dynamic ranges from 1.0×10(-7) to 1.0×10(-6)M and 1.0×10(-6) to 1.0×10(-4)M with a detection limit of (4.5±0.18)×10(-8)M. A 100-fold excess of serotonin, acetaminophen, folic acid, uric acid, tryptophan, tyrosine and cysteine, 10-fold excess of ascorbic acid and twofold excess of dopamine do not interfere in the quantification of EP at this electrode. The analytical applications of the modified electrode were demonstrated by determining EP in spiked blood serum and adrenaline tartrate injection. The modified electrode involves a simple fabrication procedure, minimum usage of the modifier, quick response, excellent stability, reproducibility and anti-fouling effects. PMID:24840456

We dispersed the non-covalent functionalization of multi-walledcarbon nanotubes (CNTs) with a polymer dispersant and obtained a powder of polymer-wrapped CNTs. The UV–vis absorption spectrum was used to investigate the optimal weight ratio of the CNTs and polymer dispersant. The powder of polymer-wrapped CNTs had improved the drawbacks of CNTs of being lightweight and difficult to process, and it can re-disperse in a solvent. Then, we blended the polymer-wrapped CNTs and polyethylene (PE) by melt-mixing and produced a conductive masterbatch and CNT/PE composites. The polymer-wrapped CNTs showed lower surface resistivity in composites than the raw CNTs. The scanning electron microscopy images also showed that the polymer-wrapped CNTs can disperse well in composites than the raw CNTs. PMID:22559082

H2S and SO2 are important characteristic gases of partial discharge (PD) generated by latent insulated defects in gas insulated switchgear (GIS). The detection of H2S and SO2 is of great significance in the diagnosis and assessment of the operating status of GIS. In this paper, we perform experiments on the gas sensitivity of unmodified multi-walledcarbon nanotubes (MWNTs) and those modified by atmospheric pressure dielectric barrier discharge (DBD) air plasma at different times (30, 60 and 120 s) for H2S and SO2, respectively. The results show that the sensitivity and response time of modified MWNTs to H2S are both improved, whereas the opposite effects are observed for SO2. The modified MWNTs have almost zero sensitivity to SO2. Thus, the MWNTs modified by atmospheric pressure DBD air plasma present good selectivity to H2S, and have great potential in H2S detection. PMID:23012548

Rodlike thermotropic liquid crystalline polyester (TLCP) was synthesized from 4,4'-oxydibenzoyl chloride and resorcinol containing modified multi-walledcarbon nanotubes (MWCNTs) by in situ high-temperature solution polymerization. The liquid crystalline properties and thermal stability of the resulted TLCP nanocomposites were characterized by XRD, DSC, TGA, SEM, POM, and optical analysis. The addition of small amount of MWCNTs into TLCP matrix could significantly improve the thermal stability. The mesophase temperature range of nanocomposites were widened and shifted to higher temperatures. This nanocomposite melting phase transition ( Tm) value increases maximally to 38.4 °C compared with pure copolymer. Using the Horowits-Metzger kinetic method, the PE/M-0.5 gave the best performance in terms of the thermal stability. This result can be explained that the incorporation of MWCNTs into TLCP caused an interaction between TLCP and MWCNTs through π-π* conjugation.

Multi-walledcarbon nanotubes (MWCNTs) are easily wrapped with a functional biopolymer—polydopamine (Pdop) through self-polymerization of dopamine in a mild basic solution. The MWCNTs@Pdop exhibits long term dispersivity in water for at least one month. The Pdop has large capacity to coordinate [PdCl 4] 2- and [PtCl 6] 2- that upon reduction transform to corresponding metal nanoparticles. The nanoparticles strongly adhere to Pdop layer and can be used for the electrooxidation of haydrazine and methanol, respectively. Compared to Pd and Pt supported on unmodified MWCNTs, the Pd and Pt nanoparticle decorated on MWCNTs@Pdop exhibit much higher electrocatalytic activity and enhanced stability.

Multi-walledcarbon nanotubes (MWNTs) were synthesized by irradiating of a CO2 laser in continuous wave mode onto a boron-containing graphite target at room temperature. The pressure of Ar atmosphere was controlled in 50, 150, 400, or 760 Torr. The diameter of obtained MWNTs was in the range of 5-40 nm. The quantity and degree of graphitization of synthesized MWNTs increased with the Ar gas pressure. A large quantity of MWNTs with fine crystalline structure has been synthesized preferentially at the condition of 760 Torr. The MWNTs with the fine crystalinity indicated highly oxidative stability in O2. We also found that a large area field emission device with MWNT cathodes indicated good β value of 3.6 × 104 cm-1, and sufficient reliability for long term operations over 150 h, suggesting promising application to field emission devices.

Biocompatible polymer nanofibers hold great potential in the biomedical engineering field. Their biodegradable nature and enhanced properties could help solve a wide array of health related problems, particularly in the areas of tissue regeneration, drug delivery, and biosensor design. The novel Forcespinning™ method allows the production of submicron fibers without many of the drawbacks found in electrospinning, while also providing a substantial increase in fiber production. The aim of the study was to utilize this method to fabricate non-woven nanofibrous mats composed of polylactic acid (PLA) and polylactic acid/multi-walledcarbon nanotube composite fibers. The morphology, thermal properties, and crystalline structure of the resulting nanofibers were then characterized using Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), and X-Ray Diffraction (XRD).

Single-crystal {alpha}-MnO{sub 2} nanorods were grown on multi-walledcarbon nanotubes (MWNTs) in H{sub 2}SO{sub 4} aqueous solution. The morphology and microstructure of the composites were examined by transmission electron microscopy, high-resolution transmission electron microscopy (HRTEM), X-ray diffractometry and energy dispersive spectroscopy (EDS). The results show that {alpha}-MnO{sub 2} single-crystal nanorods with a mean diameter of 15 nm were densely grown on the surface of MWNTs. Those MWNTs/MnO{sub 2} composites were used as an electrode material for supercapacitors, and it was found that the supercapacitor performance using MWNTs/MnO{sub 2} composites was improved largely compared to that using pure MWNTs and {alpha}-MnO{sub 2} nanorod mechanically mixed with MWNTs.

Low color visibility and poor mechanical strength of polystyrene (PS) photonic crystal films have been the main shortcomings for the potential applications in paints or displays. This paper presents a simple method to fabricate PS/MWCNTs (multi-walledcarbon nanotubes) composite photonic crystal films with enhanced color visibility and mechanical strength. First, MWCNTs was modified through radical addition reaction by aniline 2,5-double sulfonic acid diazonium salt to generate hydrophilic surface and good water dispersity. Then the MWCNTs dispersion was blended with PS emulsion to form homogeneous PS/MWCNTs emulsion mixtures and fabricate composite films through thermal-assisted method. The obtained films exhibit high color visibility under natural light and improved mechanical strength owing to the light-adsorption property and crosslinking effect of MWCNTs. The utilization of MWCNTs in improving the properties of photonic crystals is significant for various applications, such as in paints and displays. PMID:27136514

We investigated the effect of plasma-treated multi-walledcarbon nanotubes (CNTs) that are composited into a polyurethane (PU) film. In this journal article, we especially focused on one of mechanical properties of PU film, the wear resistance, to find how the plasma-treated CNTs give contributions to improve the resistance. Our experimental results showed that plasma-treated CNTs enhanced the wear resistance, in particular, when the CNTs treated with the plasma that was made of nitrogen-oxygen mixture gas. Then, we made measurements with infrared absorption spectroscopy to find the possible causes of the improvement. The measurement showed that the surface of the CNTs treated with nitrogen-oxygen plasma had an indication of isocyanate group, which generally hardens PU film. The plasma likely attached the functional group on CNTs, and then the CNTs added extra wear resistance of a polyurethane film.

Composites based on multi-walledcarbon nanotubes (MWCNTs)s and poly(L-lactide) (PLLA) were prepared by using solvent casting method. Both carboxylated MWCNTs and pristine MWCNTs were considered in order to investigate the interactions between PLLA and MWCNTs and to understand the role of the filler in the biodegradability. In vitro degradation studies were performed by measurement of weight loss, FT-IR, DSC and SEM over a 30 weeks period. Pristine MWCNTs and carboxylated MWCNTs had a different effect on the degradation of PLLA. Thermal properties of MWCNTs based PLLA composites changed compared to neat PLLA. A possible mechanism of MWCNTs effect on the degradation of PLLA was discussed.

A novel chiral electrochemical sensor based on multi-walledcarbon nanotubes (MWCNTs)/ionic liquids (ILs) nanocomposite was developed and applied to the enantiomeric recognition of propranolol (PRO). Mechanisms for chiral sensing were discussed in terms of the formation of an efficient chiral nanospace originating from the weak interactions between quasi-chiral MWCNTs and versatile ILs. This work provided new evidence that the electro-oxidation of PRO should result from its hydroxyl group. Herein the ratio of oxidation peak currents, instead of the commonest shift of peak potential, was used to sense the enantiomeric fraction (EF) of (R)-PRO with a linear correlation coefficient of 0.9936. This simple and reliable sensor was successfully applied in an accurate determination of the enantiomeric purity of reagent, as well as the evaluation of waste water treatment efficiency. PMID:23598015

We observed that nanowires of Fe grown in the lumens of multi-walledcarbon nanotubes required four times higher magnetic field strength to reach saturation compared to planar nanometric thin films of Fe on MgO(100). Nanowires of Fe and nanometric thin films of Fe both exhibited two fold magnetic symmetries. Structural and magnetic properties of 1-dimensional nanowires and 2-dimensional nanometric films were studied by several magnetometery techniques. The θ-2θ x-ray diffraction measurements showed that a (200) peak of Fe appeared on thin film samples deposited at higher substrate temperatures. In these samples prepared at higher temperatures, lower coercive field and highly pronounced two-fold magnetic symmetry were observed. Our results show that maximum magnetocrystalline anisotropy occurred for sample deposited at 100 °C and it decreased at higher deposition temperatures.

Multi-walledcarbon nanotubes (MWCNTs) were functionalized by monoethanolamine (MEA), diethanolamine (DEA) and triethanolamine (TEA) by a rapid microwave-assisted method. Surface functional groups and morphology of MWCNTs were analyzed by ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, Raman spectroscopy and transmission electron microscopy. The water dispersibility of samples was also measured over time and compared with that of MWCNT functionalized by ethylenediamine (EDA). Accordingly, the dispersibility was in the sequence MEA-MWCNTs > DEA-MWCNTs > TEA-MWCNTs > EDA-MWCNTs > pristine MWCNTs. The significant long-term dispersibility of MEA-MWCNTs was related to its exceptionally high surface functionalization (89.3 %) and lack of chemical bridging between adjacent MWCNTs. This strategy, along with the low-cost functionalizing agents, could pave the way for large-scale dispersion of CNTs in the polar solvents.

A multi-walledcarbon nanotubes-polypyrrole conducting polymer nanocomposite has been synthesized, characterized and used for the separation and preconcentration of lead at trace levels in water samples prior to its flame atomic absorption spectrometric detection. The analytical parameters like pH, sample volume, eluent, sample flow rate that were affected the retentions of lead(II) on the new nanocomposite were optimized. Matrix effects were also investigated. Limit of detection and preconcentration factors were 1.1 µg L(-1) and 200, respectively. The adsorption capacity of the nanocomposite was 25.0mg lead(II) per gram composite. The validation of the method was checked by using SPS-WW2 Waste water Level 2 certified reference material. The method was applied to the determination of lead in water samples with satisfactory results. PMID:24401439

The dehydrogenation kinetics of LiBH4 dispersed on multi-walledcarbon nanotubes (MWCNTs) by the solvent infiltration technique has been studied. Commercial MWCNTs were ball-milled for different milling times in order to increase the specific surface area (SSA) as measured by the BET technique. Thermal programmed desorption measurements have been performed using a Sievert's apparatus on samples with different SSA of MWCNTs and different LiBH4 to MWCNT ratio. Pressure composition isotherms (PCI) have been obtained at different temperatures in order to estimate the ΔH and ΔS of dehydrogenation. It has been observed that the dispersion of LiBH4 on MWCNTs leads to a lower dehydrogenation temperature compared to pure LiBH4. Moreover, the dehydrogenation temperature further decreases with increasing MWCNT surface area. An interpretation of the kinetic effect is proposed.

Due to the fibrous shape and durability of multi-walledcarbon nanotubes (MWCNT), concerns regarding their potential for producing environmental and human health risks, including carcinogenesis, have been raised. This study sought to investigate how previously identified lung cancer prognostic biomarkers and the related cancer signaling pathways are affected in the mouse lung following pharyngeal aspiration of well-dispersed MWCNT. A total of 63 identified lung cancer prognostic biomarker genes and major signaling biomarker genes were analyzed in mouse lungs (n = 80) exposed to 0, 10, 20, 40, or 80 {mu}g of MWCNT by pharyngeal aspiration at 7 and 56 days post-exposure using quantitative PCR assays. At 7 and 56 days post-exposure, a set of 7 genes and a set of 11 genes, respectively, showed differential expression in the lungs of mice exposed to MWCNT vs. the control group. Additionally, these significant genes could separate the control group from the treated group over the time series in a hierarchical gene clustering analysis. Furthermore, 4 genes from these two sets of significant genes, coiled-coil domain containing-99 (Ccdc99), muscle segment homeobox gene-2 (Msx2), nitric oxide synthase-2 (Nos2), and wingless-type inhibitory factor-1 (Wif1), showed significant mRNA expression perturbations at both time points. It was also found that the expression changes of these 4 overlapping genes at 7 days post-exposure were attenuated at 56 days post-exposure. Ingenuity Pathway Analysis (IPA) found that several carcinogenic-related signaling pathways and carcinogenesis itself were associated with both the 7 and 11 gene signatures. Taken together, this study identifies that MWCNT exposure affects a subset of lung cancer biomarkers in mouse lungs. - Research Highlights: > Multi-WalledCarbon Nanotubes affect lung cancer biomarkers in mouse lungs. > The results suggest potentially harmful effects of MWCNT exposure on human lungs. > The results could potentially be used for

Uptake and translocation of short functionalized multi-walledcarbon nanotubes (short-fMWCNTs) through the pulmonary respiratory epithelial barrier depend on physicochemical property and cell type. Two monoculture models, immortalized human alveolar epithelial type 1 (TT1) cells and primary human alveolar epithelial type 2 cells (AT2), which constitute the alveolar epithelial barrier, were employed to investigate the uptake and transport of 300 and 700 nm in length, poly(4-vinylpyridine)-functionalized, multi-walledcarbon nanotubes (p(4VP)-MWCNTs) using quantitative imaging and spectroscopy techniques. The p(4VP)-MWCNT exhibited no toxicity on TT1 and AT2 cells, but significantly decreased barrier integrity (*p < 0.01). Uptake of p(4VP)-MWCNTs was observed in 70% of TT1 cells, correlating with compromised barrier integrity and basolateral p(4VP)-MWCNT translocation. There was a small but significantly greater uptake of 300 nm p(4VP)-MWCNTs than 700 nm p(4VP)-MWCNTs by TT1 cells. Up to 3% of both the 300 and 700 nm p(4VP)-MWCNTs reach the basal chamber; this relatively low amount arose because the supporting transwell membrane minimized the amount of p(4VP)-MWCNT translocating to the basal chamber, seen trapped between the basolateral cell membrane and the membrane. Only 8% of AT2 cells internalized p(4VP)-MWCNT, accounting for 17% of applied p(4VP)-MWCNT), with transient effects on barrier function, which initially fell then returned to normal; there was no MWCNT basolateral translocation. The transport rate was MWCNT length modulated. The comparatively lower p(4VP)-MWCNT uptake by AT2 cells is proposed to reflect a primary barrier effect of type 2 cell secretions and the functional differences between the type 1 and type 2 alveolar epithelial cells. PMID:27035850

In an effort to combine group III-V semiconductors with carbon nanotubes, a simple solution-based technique for gallium functionalization of nitrogen-doped multi-wallcarbon nanotubes has been developed. With an aqueous solution of a gallium salt (GaI(3)), it was possible to form covalent bonds between the Ga(3+) ion and the nitrogen atoms of the doped carbon nanotubes to form a gallium nitride-carbon nanotube hybrid at room temperature. This functionalization was evaluated by x-ray photoelectron spectroscopy, energy dispersive x-ray spectroscopy, Raman spectroscopy, scanning electron microscopy and transmission electron microscopy. PMID:22825368

A novel 2-dimensional graphene analog molybdenum disulfide/multi-walledcarbon nanotube (MoS2/MWCNT) was synthesized by a simple hydrothermal method to achieve excellent electrochemical properties. An ultrasensitive electrochemical DNA biosensor was subsequently constructed by assembling a thiol-tagged DNA probe on a MoS2/MWCNT and gold nanoparticle (AuNP)-modified electrode that has already been coupled with glucose oxidase (GOD). In this work, GOD was used as a redox marker. The heteronanostructure formed on the biosensor surface appeared relatively good conductor for accelerating the electron transfer, while the modification of GOD and AuNPs provided multiple signal amplification for electrochemical biosensing. The multiple signal amplification strategy produced an ultrasensitive electrochemical detection of DNA down to 0.79 fM with a linear range from 10 fM to 10(7)fM, and appeared high selectivity to differentiate three-base mismatched DNA and one-base mismatched DNA. The developed approach provided a simple and reliable method for DNA detection with high sensitivity and specificity, and would open new opportunities for sensitive detection of other biorecognition events. PMID:24384259

In this work, poly(methyl methacrylate) (PMMA) was grafted onto amine treated multi-walledcarbon nanotubes (NH-MWNTs) and the physical and rheological properties of the NH-MWNTs-g-PMMA nanocomposites were investigated. The graft reaction of NH-MWNTs and the PMMA matrix was confirmed from the change of the N{sub 1S} peaks, including those of amine oxygen and amide oxygen, by X-ray photoelectron spectroscopy (XPS). The thermal and mechanical properties of the NH-MWNT-g-PMMA nanocomposites were enhanced by the graft reaction between NH-MWNTs and PMMA matrix. In addition, the viscosity of the nanocomposites was increased with the addition of NH-MWNTs. Storage (G') and loss modulus (G'') were significantly increased by increase in the NH-MWNT content compared to acid-treated MWNTs/PMMA nanocomposites. This increase was attributed to the strong interaction by the grafting reaction between NH-MWNTs and the PMMA matrix. - Graphical abstract: This describes the increase of mechanical properties in NH-MWNTs-g-PMMA hybrid composites with different NH-MWNT contents. Highlights: > Aminized carbon nanotubes are used as reinforcement for poly(methylmethacrylate). > Poly(methylmethacrylate) is grafted on aminized carbon nanotubes by thermal reaction. > Grafting of carbon nanotubes and polymer provide enhanced physical properties. > It was due to the strong interaction between carbon nanotubes and polymer matrix.

Chemoresistive sensors based on multi-walledcarbon nanotubes (MWCNTs)functionalized with SnO2 nanocrystals have great potential for detecting trace gases at low concentrations (single ppm levels) at room temperature, because the SnO2 nanocrystals act as active sites for the chem...

Carbon nanotubes have received a great attention in the last years thanks to their remarkable structural, electrical, and chemical properties. Nowadays carbon nanotubes are increasingly found in terrestrial and aquatic environment and potential harmful impacts of these nanoparticles on humans and wildlife are attracting increasing research and public attention. The effects of carbon nanotubes on aquatic organisms have been explored by several authors, but comparatively the information available on the impact of these particles on soil organisms is much less. Earthworms have traditionally been considered to be convenient indicators of land use impact and soil fertility. The aim of this work was to study the integrated response of a suite of biomarkers covering molecular to whole organism endpoints for the assessment of multi-walledcarbon nanotube (MWCNTs) effects on earthworms (Eisenia fetida) exposed to spiked soil. Results showed that cellular and biochemical responses, such as immune cells morphometric alterations and lysosomal membrane destabilization, acetylcholinesterase inhibition and metallothionein tissue concentration changes, showed high sensitivity to MWCNTs exposure. They can improve our understanding and ability to predict chronic toxicity outcomes of MWCNTs exposure such as reproductive alterations. In this context although more investigation is needed to understand the mechanistic pathway relating the biochemical and cellular biomarker analyzed to reproductive alterations, the obtained results give an early contribution to the future development of an adverse outcomes pathways for MWCNTs exposure. PMID:26892788

The aim of the study was to fabricate and extensively characterize a layer of carbon nanotubes deposited on the surface of titanium, in order to prove that, by selecting proper type of carbon nanotubes and altering different parameters of the electrophoretic deposition process, we are able to obtain products having a different influence on cells—either favouring or inhibiting their survival. In the study, a novel mixture of solvents was used to suspend as-received tubes and then applied in the electrophoretic deposition. High charging capability and high yield of the obtained deposits are promising results when considering up-scaling the process. The surface of the obtained multi-walledcarbon nanotubes-coated titanium samples was characterized using SEM, AFM, XPS and Raman microspectroscopy. The carbon nanotube layer showed nanorough topography and was formed of randomly and loosely distributed tubes, and XPS study revealed that there was a significant amount of C-O bonds. These properties were found to be favourable to osteoblast survival, spreading and growth.

Highlights: •HTT2800-treated BEAS-2B cells induced LC3B in a time-dependent manner. •HTT2800-treated BEAS-2B cells showed decreased cell proliferation that was both time- and dose-dependent. •Addition of 3-MA, LC3B-II protein and mRNA levels were significantly decreased. •3-MA and E64-d + pepstatin A, but not brefeldin A, provided protection against HTT2800-induced cell death. •These results suggest that HTT2800 predominantly causes autophagy rather than apoptotic cell death in BEAS-2B cells. -- Abstract: Bronchial epithelial cells are targets of inhalation and play a critical role in the maintenance of mucosal integrity as mechanical barriers against various particles. Our previous result suggest that vapor-grown carbon fiber, HTT2800, which is one of the most highly purified multi-wallcarbon nanotubes (MWCNT) showed cellular uptake of the carbon nanotube, increased cell death, enhanced DNA damage, and induced cytokine release. Increasing evidence suggests that autophagy may critically influence vital cellular processes such as apoptosis, cell proliferation and inflammation and thereby may play a critical role in pulmonary diseases. Autophagy was recently recognized as a critical cell death pathway, and autophagosome accumulation has been found to be associated with the exposure of various nanoparticles. In this study, the authors focus on the autophagic responses of HTT2800 exposure. The HTT2800-exposed cells induced LC3B expression and induced cell growth inhibition.

With the aim of improving the amount and delivery efficiency of genes taken by carbon nanotubes into human cancer cells, different generations of polyamidoamine dendrimer modified multi-walledcarbon nanotubes (dMNTs) were fabricated, and characterized by high-resolution transmission electron microscopy, atomic force microscopy, x-ray photoelectron spectroscopy, Raman spectroscopy, Fourier transform infrared spectroscopy and thermogravimetric analysis, revealing the presence of dendrimer capped on the surface of carbon nanotubes. The dMNTs fully conjugated with FITC-labeled antisense c-myc oligonucleotides (asODN), those resultant asODN-dMNTs composites were incubated with human breast cancer cell line MCF-7 cells and MDA-MB-435 cells, and liver cancer cell line HepG2 cells, and confirmed to enter into tumor cells within 15 min by laser confocal microscopy. These composites inhibited the cell growth in time- and dose-dependent means, and down-regulated the expression of the c-myc gene and C-Myc protein. Compared with the composites of CNT-NH2-asODN and dendrimer-asODN, no. 5 generation of dendrimer-modified MNT-asODN composites exhibit maximal transfection efficiencies and inhibition effects on tumor cells. The intracellular gene transport and uptake via dMNTs should be generic for the mammalian cell lines. The dMNTs have potentials in applications such as gene or drug delivery for cancer therapy and molecular imaging.

The impacts of carbon nanotubes (CNTs) including single-walled carbon nanotubes (SWNTs) and multi-walledcarbon nanotubes (MWNTs) on soil microbial biomass and microbial community composition (especially on ammonium oxidizing microorganisms) have been evaluated. The first exposure of CNTs lowered the microbial biomass immediately, but the values recovered to the level of the control at the end of the experiment despite the repeated addition of CNTs. The abundance and diversity of ammonium-oxidizing archaea (AOA) were higher than that of ammonium-oxidizing bacteria (AOB) under the exposure of CNTs. The addition of CNTs decreased Shannon-Wiener diversity index of AOB and AOA. Two-way ANOVA analysis showed that CNTs had significant effects on the abundance and diversity of AOB and AOA. Dominant terminal restriction fragments (TRFs) of AOB exhibited a positive relationship with NH4(+), while AOA was on the contrary. It implied that AOB prefer for high-NH4(+) soils whereas AOA is favored in low NH4(+) soils in the CNT-contaminated soil. PMID:25461068

The adsorption characteristics of 4-chloro-2-nitrophenol (4C2NP) onto single-walled and multi-walledcarbon nanotubes (SWCNTs and MWCNTs) from aqueous solution were investigated with respect to the changes in the contact time, pH of solution, carbon nanotubes dosage and initial 4C2NP concentration. Experimental results showed that the adsorption efficiency of 4C2NP by carbon nanotubes (both of SWCNTs and MWCNTs) increased with increasing the initial 4C2NP concentration. The maximum adsorption took place in the pH range of 2–6. The linear correlation coefficients of different isotherm models were obtained. Results revealed that the Langmuir isotherm fitted the experimental data better than the others and based on the Langmuir model equation, maximum adsorption capacity of 4C2NP onto SWCNTs and MWCNTs were 1.44 and 4.42 mg/g, respectively. The observed changes in the standard Gibbs free energy, standard enthalpy and standard entropy showed that the adsorption of 4C2NP onto SWCNTs and MWCNTs is spontaneous and exothermic in the temperature range of 298–328 K. PMID:23369489

We have designed a novel hybrid nanostructure by coating Fe2O3 nanoparticles with multi-walledcarbon nanotubes to enhance the lithium storage capability of Fe2O3. The strategy to prepare Fe2O3@MWCNTs involves the synthesis of Fe nanoparticles wrapped in MWCNTs, followed by the oxidation of Fe nanoparticles under carbon dioxide. When used as the anode in a Li-ion battery, this hybrid material (70.32 wt% carbon nanotubes, 29.68 wt% Fe2O3) showed a reversible discharge capacity of 515 mAhg−1 after 50 cycles at a density of 100 mAg−1 and the capacity based on Fe2O3 nanoparticles was calculated as 1147 mAhg−1, Three factors are responsibile for the superior performance: (1) The hollow interiors of MWCNTs provide enough spaces for the accommodation of large volume expansion of inner Fe2O3 nanoparticles, which can improving the stability of electrode; (2) The MWCNTs increase the overall conductivity of the anode; (3) A stable solid electrolyte interface film formed on the surface of MWCNTs may reduce capacity fading. PMID:24292097

A simple and highly sensitive sensor for the determination of diclofenac sodium based on gold nanoparticle/multi-walledcarbon nanotube modified glassy carbon electrode is reported. Scanning electron microscopy along with energy dispersive X-ray spectroscopy, electrochemical impedance spectroscopy, cyclic voltammetry and square wave voltammetry was used to characterize the nanostructure and performance of the sensor and the results were compared with those obtained at the multi-walledcarbon nanotube modified glassy carbon electrode and bare glassy carbon electrode. Under the optimized experimental conditions diclofenac sodium gave linear response over the range of 0.03-200μmolL(-1). The lower detection limits were found to be 0.02μmolL(-1). The effect of common interferences on the current response of DS was investigated. The practical application of the modified electrode was demonstrated by measuring the concentration of diclofenac sodium in urine and pharmaceutical samples. This revealed that the gold nanoparticle/multiwalled carbon nanotube modified glassy carbon electrode shows excellent analytical performance for the determination of diclofenac sodium in terms of a very low detection limit, high sensitivity, very good accuracy, repeatability and reproducibility. PMID:26652361

Nanotechnology is one of the major scientific research fields in this decade. One of the most wide-spread nanomaterials are carbon based nanoparticles (CNPs) which are increasingly be used in industry. Several studies shows that CNPs are interacting with other chemical compounds and organic pollutants in the environment. It is assumed that the interactions between CNPs and organic pollutants are affected by solution and aggregate behavior. Based on the knowledge of the behavior of CNPs and organic pollutants in aquatic systems the interactions of CNPs and organic pollutants in agricultural soils have to be studied. As organic pollutants two environmental substances, nonylphenol (NP) and sodium dodecyl sulfate (SDS) were selected as model substances. They occur frequently in aqueous systems and also show different solubility behavior. As CNP representatives, two different multi-walledcarbon nanotubes (MWNT) were selected. They differed either in length or outer diameter. Conclusions therefrom are to be closed the influence of length and diameter of the sorption capacity of different organic pollutants. In addition, two agricultural soils (sandy and silty soil) and one forest soil (sandy soil) were chosen. Mineralization and sorption experiments were conducted to provide information about the degradation of organic pollutants in presence of multi-walledcarbon nanotubes in soils. To analyze the CNPs mineralization potential, peroxidase activity was measured. Further extraction experiments were conducted to detect the extractable part of organic pollutants. The results show that the surface area of the MWNT has a significant impact on the sorption behav-ior of NP and SDS in soils. The sorption of NP and SDS is much higher than without MWNT. However, the properties of the organic pollutants (different water solubility and hydrophobicity) are equally important and should be noted. The degradation of both pollutants is influenced by MWNT. Due to the strong sorption of

Nanocomposite fibers based on multi-walledcarbon nanotubes (MWCNT) and poly(lactic acid) (PLA) were prepared by solution blow spinning (SBS). Fiber morphology was characterized by scanning electron microscopy (SEM) and optical microscopy (OM). Electrical, thermal, surface and crystalline properties of the spun fibers were evaluated, respectively, by conductivity measurements (4-point probe), thermogravimetric analyses (TGA), differential scanning calorimetry (DSC), contact angle and X-ray diffraction (XRD). OM analysis of the spun mats showed a poor dispersion of MWCNT in the matrix, however dispersion in solution was increased during spinning where droplets of PLA in solution loaded with MWCNT were pulled by the pressure drop at the nozzle, producing PLA fibers filled with MWCNT. Good electrical conductivity and hydrophobicity can be achieved at low carbon nanotube contents. When only 1 wt% MWCNT was added to low-crystalline PLA, surface conductivity of the composites increased from 5 x 10(-8) to 0.46 S/cm. Addition of MWCNT can slightly influence the degree of crystallinity of PLA fibers as studied by XRD and DSC. Thermogravimetric analyses showed that MWCNT loading can decrease the onset degradation temperature of the composites which was attributed to the catalytic effect of metallic residues in MWCNT. Moreover, it was demonstrated that hydrophilicity slightly increased with an increase in MWCNT content. These results show that solution blow spinning can also be used to produce nanocomposite fibers with many potential applications such as in sensors and biosensors. PMID:22755116

Carbon nanotubes (CNTs) have been one of the widely manufactured nanoparticles which incorporate into various consumer products, such as bicycle frame, tennis racket, and other biomedical applications. After its increased production and use in several products, CNTs may create a potential environmental risk to soil and groundwater system. It is therefore essential to improve the current understanding of environmental fate and transport of CNTs at an extreme subsurface condition. It is possible that the nanoparticle can aggregate or deposit at the solid surfaces at different background chemistry and nanoparticle concentration while moving into the porous media. The current study systematically investigates the effect of inflow concentration of functionalized multi-walledcarbon nanotubes (MWCNTs) on change in retention on the solid surfaces using a series of column experiments under fully saturated condition. A one-dimensional convection-dispersion model incorporated with collector efficiency for cylindrical nanoparticles was used to simulate the transport of MWCNTs in porous media. The result showed that higher particle number concentration led to higher relative retention. It is caused by possible aggregation within the soil pores but not influenced by greater surface coverage due to higher inflow concentration.

Many potential applications of carbon nanotubes (CNTs) require various physicochemical modifications prior to use, suggesting that nanotubes having varied properties may pose risks in ecosystems. A means for estimating bioaccumulation potentials of variously modified CNTs for incorporation in predictive fate models would be highly valuable. An approach commonly used for sparingly soluble organic contaminants, and previously suggested for use as well with carbonaceous nanomaterials, involves measurement of their octanol-water partitioning coefficient (KOW) values. To test the applicability of this approach, a methodology was developed to measure apparent octanol-water distribution behaviors for purified multi-walledcarbon nanotubes and those acid treated. Substantial differences in apparent distribution coefficients between the two types of CNTs were observed, but these differences did not influence accumulation by either earthworms (Eisenia foetida) or oligochaetes (Lumbriculus variegatus), both of which showed minimal nanotube uptake for both types of nanotubes. The results suggest that traditional distribution behavior-based KOW approaches are likely not appropriate for predicting CNT bioaccumulation. PMID:20821546

DNA vaccines are considered to be the most promising method against infectious diseases in the aquaculture industry. In the present study, we investigated the potency of ammonium group-functionalized multi-walledcarbon nanotubes (MWCNTs) in enhancing the transfection and expression efficiency of plasmid DNA (pEGFP-vp5) in Ctenopharyngodon idellus kidney (CIK) cells. Agarose gel shift assay results show that ammonium group-functionalized carbon nanotubes are able to condense DNA in varying degrees. Scanning electron microscope (SEM) images shows that CIK cells show a great affinity for MWCNTs-NH₃⁺ and the CNTs covering the cell surface tend to orient their tips perpendicularly to the cell surface, and appear to be "needle-pricking the cells". Transmission electron microscope (TEM) images confirmed that MWCNTs-NH₃⁺ penetrate the cell membranes and are widely dispersed in the CIK cell. Real-time PCR was used to detect the transfection efficiency through the expression of the outer capsid protein (VP5). The results showed that the MWCNTs-NH₃⁺:DNA complexes are able to transfect CIK cells effectively at different charge ratio than naked DNA. Subsequent studies confirmed that both functional groups and charge ratio are important factors that determine the transfection efficiency of plasmid DNA. All these results indicated that MWCNTs-NH₃⁺:DNA complexes could be suitable for developing DNA vaccine for the control of virus infection in the aquaculture industry. PMID:26950121

Effect of mechanical alloying/milling on microstructural evolution and hardness variations of garnet and multi-walledcarbon nanotubes (MWCNTs)-reinforced Al-Mg-Si alloy (EN AW6082) composites are investigated. Structural and morphological studies revealed that the composite powders prepared by milling display a more homogenous distribution of the reinforcing particles. Improved nanoindentation hardness viz., 4.24 and 5.90 GPa are achieved for EN AW6082/Garnet and EN AW6082/MWCNTs composites, respectively, and it is attributed to severe deformation of the aluminum alloy powders and embedding of the harder reinforcement particles uniformly into the aluminum alloy matrix. However, enhancement in case of MWCNTs-reinforced composite makes apparent the effect of its nanosized uniform dispersion in the matrix, thereby resisting the plastic deformation at lower stress and increased dislocation density evolved during high-energy ball milling. The results of the present study indicate that carbon nanotubes and garnet can be effectively used as reinforcements for Al-based composites.

The influence of bacteria on the transport and deposition behaviors of carbon nanotubes (CNTs) in quartz sand was examined in both NaCl (5 and 25 mM ionic strength) and CaCl2 (0.3 and 1.2 mM ionic strength) solutions at unadjusted pH (5.6-5.8) by direct comparison of both breakthrough curves and retained profiles in both the presence and absence of bacteria. Two types of widely utilized CNTs, i.e., carboxyl- and hydroxyl-functionalized multi-walledcarbon nanotubes (MWCNT-COOH and MWCNT-OH, respectively), were employed as model CNTs and Escherichia coli was utilized as the model bacterium. The results showed that, for both types of MWCNTs under all examined conditions, the breakthrough curves were higher in the presence of bacteria, while the retained profiles were lower, indicating that the co-presence of bacteria in suspension increased the transport and decreased the deposition of MWCNTs in porous media, regardless of ionic strength or ion valence. Complementary characterizations and extra column tests demonstrated that competition by bacteria for deposition sites on the quartz sand surfaces was a major (and possibly the sole) contributor to the enhanced MWCNTs transport in porous media. PMID:27038577

In this report, titanium nitride (TiN) nanoparticles decorated multi-walledcarbon nanotube (MWCNTs) nanocomposite is fabricated via a two-step process. These two steps involve the decoration of titanium dioxide nanoparticles onto the MWCNTs surface and a subsequent thermal nitridation. Transmission electron microscopy shows that TiN nanoparticles with a mean diameter of ≤ 20 nm are homogeneously dispersed onto the MWCNTs surface. Direct electrochemistry and electrocatalysis of cytochrome c immobilized on the MWCNTs-TiN composite modified on a glassy carbon electrode for nitrite sensing are investigated. Under optimum conditions, the current response is linear to its concentration from 1 µM to 2000 µM with a sensitivity of 121.5 µA µM(-1)cm(-2) and a low detection limit of 0.0014 µM. The proposed electrode shows good reproducibility and long-term stability. The applicability of the as-prepared biosensor is validated by the successful detection of nitrite in tap and sea water samples. PMID:26748372

In this work, a novel amperometric immunosensor based on multi-walledcarbon nanotubes-thionine-chitosan (MWCNTs-THI-CHIT) nanocomposite film as electrode modified material was developed for the detection of chlorpyrifos residues. The nanocomposite film was dropped onto a glassy carbon electrode (GCE), and then the anti-chlorpyrifos monoclonal antibody was covalently immobilized onto the surface of MWCNTs-THI-CHIT/GCE using the crosslinking agent glutaraldehyde (GA). The modification procedure was characterized by using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Under the optimized conditions, a linear relationship between the relative change in peak current of different pulse voltammetry (DPV) and the logarithm of chlorpyrifos solution concentration was obtained in the range from 0.1 to 1.0 × 105 ng/mL with a detection limit of 0.046 ng/mL. The proposed chlorpyrifos immunosensor exhibited high reproducibility, stability, and good selectivity and regeneration, making it a potential alternative tool for ultrasensitive detection of chlorpyrifos residues in vegetables and fruits. PMID:23443396

Chitosan solutions and cellulose nanocrystal suspensions were used to produce highly stable aqueous dispersions of multi-walledcarbon nanotubes (MWCNTs). The different MWCNT dispersions, presenting positive and negative charges, were used to prepare multilayered hybrid thin films through electrostatic layer-by-layer (LBL) self-assembly. The MWCNTs are well dispersed and homogeneously distributed on each layer of chitosan and cellulose nanocrystals of the films. The nanotubes are densely packed in each multilayer, forming a random network. The surface of the LBL film exhibited a uniform and relatively smooth surface with a mean roughness value of ∼5.8±0.4nm. Electrochemical characterization revealed a decrease in two orders of magnitude in the film resistance as the number of bilayers increased from 5 to 20, which is a consequence of an increase in the amount of conductive material (MWCNT). The thin films with up to 20 bilayers exhibited transmittance higher than 90% in the visible range. The results presented in this work demonstrate the viability of the LBL technique for the deposition of active materials using the biopolymer pair chitosan/cellulose nanocrystals. The obtained films can be employed for the design of transparent and biocompatible carbon nanostructured based electrodes. PMID:25086396

The purpose of this communication is to elucidate the key role of NADPH oxidase in NLRP3 inflammasome activation and generation of pulmonary fibrosis by multi-walledcarbon nanotubes (MWCNTs). Although it is known that oxidative stress plays a role in pulmonary fibrosis by single-walled CNTs, the role of specific sources of reactive oxygen species (ROS), including NADPH oxidase, in inflammasome activation remains to be clarified. In this study, three long aspect ratio (LAR) materials (MWCNTs, SWCNTs, and silver nanowires) are used to compare with spherical carbon black and silver nanoparticles for their ability to trigger oxygen burst activity and NLRP3 assembly. All LAR materials but not spherical nanoparticles induce robust NADPH oxidase activation and respiratory burst activity in THP-1 cells, which are blunted in p22phox deficient cells. NADPH oxidase is directly involved in lysosome damage by LAR materials, as demonstrated by decreased cathepsin B release and IL-1β production in p22phox deficient cells. Reduced respiratory burst activity and inflammasome activation are also observed in bone marrow-derived macrophages from p47phox deficient mice. Moreover, p47phox deficient mice have reduced IL-1β production and lung collagen deposition in response to MWCNTs. Lung fibrosis is also suppressed by N-acetyl-cysteine (NAC) in wild type animals exposed to MWCNTs. PMID:25581126

One of the main questions limiting application of fibrous carbon nanomaterials (CNM) in medicine and food industry concerns presumptive degradation of CNM in living organisms. In this study, we have investigated biodegradation of multi-walledcarbon nanotubes (MWCNTs) by gastric agents in vitro and influence of ingested MWCNTs on murine intestine. Using scanning, conventional transmission and analytical electron microscopy, we demonstrated that industrial MWCNTs treated in vitro by 0.1 M hydrochloric acid (pH=1) and gastric juice (pH=2-3) isolated from murine stomach, are subjected to incomplete degradation. After 30 days of oral administration to experimental mice, we did find MWCNTs in the cells of small intestine, and it may indicate that agglomerates of MWCNTs do not penetrate into colon epithelia and do not accumulate in enterocytes. However, we observed local areas of necrotic damages of intestinal villi. It seems likely, therefore, that MWCNTs end up leaving gastrointestinal tract by excretion with the feces. Our results suggest that MWCNTs do not undergo complete degradation in gastrointestinal tract of mice, and passing through non-degraded particles may negatively affect intestinal system.

In the present paper, an analytical solution based on a molecular mechanics model is developed to evaluate the elastic critical axial buckling strain of chiral multi-walledcarbon nanotubes (MWCNTs). To this end, the total potential energy of the system is calculated with the consideration of the both bond stretching and bond angular variations. Density functional theory (DFT) in the form of generalized gradient approximation (GGA) is implemented to evaluate force constants used in the molecular mechanics model. After that, based on the principle of molecular mechanics, explicit expressions are proposed to obtain elastic surface Young's modulus and Poisson's ratio of the single-walled carbon nanotubes corresponding to different types of chirality. Selected numerical results are presented to indicate the influence of the type of chirality, tube diameter, and number of tube walls in detailed. An excellent agreement is found between the present numerical results and those found in the literature which confirms the validity as well as the accuracy of the present closed-form solution. It is found that the value of critical axial buckling strain exhibit significant dependency on the type of chirality and number of tube walls. PMID:26930445

Multi-wallcarbon nanotubes (MW-CNTs) have been arranged in nanochannels of anodic aluminum oxide template (AAO) by electrophoretic deposition (EPD) to make a vertically-aligned carbon nanotube (VA-CNT) based electrode. Well ordered AAO templates were prepared by a two-step anodizing process by applying a constant voltage of 45 V in oxalic acid solution. The stabilized CNTs in a water-soluble room temperature ionic liquid (1-methyl-3-octadecylimidazolium bromide), were deposited in the pores of AAO templates which were conductive by deposition of Ni nanoparticles in the bottom of pores. In order to obtain ideal results, different EPD parameters, such as concentration of MWCNTs and ionic liquid on stability of MWCNT suspensions, deposition time and voltage which are applied in EPD process and also optimal conditions for anodizing of template were investigated. The capacitive performance of prepared electrodes was analyzed by measuring the specific capacitance from cyclic voltammograms and the charge-discharge curves. A maximum value of 50 Fg-1 at the scan rate of 20 mV s-1was achieved for the specific capacitance.

Different toxicity tests for carbon nanotubes (CNT) have been developed to assess their impact on human health and on aquatic and terrestrial animal and plant life. We present a new model, the fruit fly Drosophila embryo offering the opportunity for rapid, inexpensive and detailed analysis of CNTs toxicity during embryonic development. We show that injected DiI labelled multi-walledcarbon nanotubes (MWCNTs) become incorporated into cells in early Drosophila embryos, allowing the study of the consequences of cellular uptake of CNTs on cell communication, tissue and organ formation in living embryos. Fluorescently labelled subcellular structures showed that MWCNTs remained cytoplasmic and were excluded from the nucleus. Analysis of developing ectodermal and neural stem cells in MWCNTs injected embryos revealed normal division patterns and differentiation capacity. However, an increase in cell death of ectodermal but not of neural stem cells was observed, indicating stem cell-specific vulnerability to MWCNT exposure. The ease of CNT embryo injections, the possibility of detailed morphological and genomic analysis and the low costs make Drosophila embryos a system of choice to assess potential developmental and cellular effects of CNTs and test their use in future CNT based new therapies including drug delivery. PMID:24558411

In this paper, two carbon nanotube (CNT) nanofillers, namely the multi-walledcarbon nanotubes (MWCNTs) and the carboxyl-modified MWCNTs (cMWCNTs), were introduced into the polydimethylsiloxane (PDMS) matrix respectively, in order to produce the PDMS composites with reinforced anti-biofouling properties. The anti-biofouling capacity of the silicone-based coatings, including the unfilled PDMS (P0), the MWCNTs-filled PDMS (PM) and the cMWCNTs-filled PDMS (PC), was examined via the field assays conducted in Weihai, China. The effect of different silicone-based coatings on the dynamic variations of the pioneer microbial-community diversity was analyzed using the single-strand conformation polymorphism (SSCP) technique. The PM and PC surfaces have exhibited excellent anti-biofouling properties in contrast to that of the PDMS surface, with extremely low attachment of the early colonizers, such as juvenile invertebrates, seaweeds and algae sporelings. The PM and PC surfaces can effectively prevent biofouling for more than 12 weeks. These combined results suggest that the incorporation of MWCNTs or cMWCNTs into the PDMS matrix can dramatically reinforce its anti-biofouling properties. The SSCP analysis reveals that compared with the PDMS surfaces, the PM and PC surfaces have strong modulating effect on the pioneer prokaryotic and eukaryotic communities, particularly on the colonization of pioneer eukaryotic microbes. The significantly reduced pioneer eukaryotic-community diversity may contribute to the weakening of the subsequent colonization of macrofoulers. PMID:27137800

DNA vaccines are considered to be the most promising method against infectious diseases in the aquaculture industry. In the present study, we investigated the potency of ammonium group-functionalized multi-walledcarbon nanotubes (MWCNTs) in enhancing the transfection and expression efficiency of plasmid DNA (pEGFP-vp5) in Ctenopharyngodon idellus kidney (CIK) cells. Agarose gel shift assay results show that ammonium group-functionalized carbon nanotubes are able to condense DNA in varying degrees. Scanning electron microscope (SEM) images shows that CIK cells show a great affinity for MWCNTs-NH3+ and the CNTs covering the cell surface tend to orient their tips perpendicularly to the cell surface, and appear to be “needle-pricking the cells”. Transmission electron microscope (TEM) images confirmed that MWCNTs-NH3+ penetrate the cell membranes and are widely dispersed in the CIK cell. Real-time PCR was used to detect the transfection efficiency through the expression of the outer capsid protein (VP5). The results showed that the MWCNTs-NH3+:DNA complexes are able to transfect CIK cells effectively at different charge ratio than naked DNA. Subsequent studies confirmed that both functional groups and charge ratio are important factors that determine the transfection efficiency of plasmid DNA. All these results indicated that MWCNTs-NH3+:DNA complexes could be suitable for developing DNA vaccine for the control of virus infection in the aquaculture industry. PMID:26950121

This paper reports the influence of milling time on the structure and properties of the precipitate catalyst of multiwalledcarbon nanotubes (MWCNT)/alumina hybrid compound, produced through the chemical vapour deposition (CVD) process. For this purpose, light green precipitate consisted of aluminium, nickel(II) nitrate hexahydrate and sodium hydroxide mixture was placed in a planetary mill equipped with alumina vials using alumina balls at 300 rpm rotation speed for various milling time (5-15 h) prior to calcinations and CVD process. The compound was characterized using various techniques. Based on high-resolution transmission electron microscopy analysis, increasing the milling time up to 15 h decreased the diameter of MWCNT from 32.3 to 13.1 nm. It was noticed that the milling time had a significant effect on MWCNT wall thickness, whereby increasing the milling time from 0 to 15 h reduced the number of walls from 29 to 12. It was also interesting to note that the carbon content increased from 23.29 wt.% to 36.37 wt.% with increasing milling time.

We employed an in vivo Caenorhabditis elegans assay system to perform SOLiD sequencing analysis to identify the possible microRNA (miRNA) targets of multi-walledcarbon nanotubes (MWCNTs). Bioinformatics analysis on targeted genes for the identified dysregulated miRNAs in MWCNT exposed nematodes demonstrates their involvement in many aspects of biological processes. We used loss-of-function mutants for the identified dysregulated miRNAs to perform toxicity assessment by evaluating functions of primary and secondary targeted organs, and found the miRNA mutants with susceptible or resistant property towards MWCNT toxicity. Both the physiological state of the intestine and defecation behavior were involved in the control of the susceptible or resistant property occurrence for specific miRNA mutants towards MWCNT toxicity. This work provides the molecular basis at the miRNA level for future chemical design to reduce the nanotoxicity of MWCNTs and further elucidation of the related toxicological mechanism.We employed an in vivo Caenorhabditis elegans assay system to perform SOLiD sequencing analysis to identify the possible microRNA (miRNA) targets of multi-walledcarbon nanotubes (MWCNTs). Bioinformatics analysis on targeted genes for the identified dysregulated miRNAs in MWCNT exposed nematodes demonstrates their involvement in many aspects of biological processes. We used loss-of-function mutants for the identified dysregulated miRNAs to perform toxicity assessment by evaluating functions of primary and secondary targeted organs, and found the miRNA mutants with susceptible or resistant property towards MWCNT toxicity. Both the physiological state of the intestine and defecation behavior were involved in the control of the susceptible or resistant property occurrence for specific miRNA mutants towards MWCNT toxicity. This work provides the molecular basis at the miRNA level for future chemical design to reduce the nanotoxicity of MWCNTs and further elucidation of the

Carbon nanotube (CNT) has a promising usage in the field of material science for industrial purposes because of its unique physicochemical property. However, intraperitoneal administration of CNT was reported to cause mesothelioma in experimental animals. Chronic inflammation may contribute to carcinogenesis induced by fibrous materials. 8-Nitroguanine is a mutagenic DNA lesion formed during inflammation and may play a role in CNT-induced carcinogenesis. In this study, we examined 8-nitroguanine formation in A549 human lung alveolar epithelial cells treated with multi-walled CNT (MWCNT) by fluorescent immunocytochemistry. Both MWCNTs with diameter of 20–30 nm (CNT20) and 40–70 nm (CNT40) significantly induced 8-nitroguanine formation at 5 and 10 μg/ml (p < 0.05), which persisted for 24 h, although there was no significant difference in DNA-damaging abilities of these MWCNTs. MWCNTs significantly induced the expression of inducible nitric oxide synthase (iNOS) for 24 h (p < 0.05). MWCNTs also significantly increased the level of nitrite, a hydrolysis product of oxidized NO, in the culture supernatant at 4 and 8 h (p < 0.05). MWCNT-induced 8-nitroguanine formation and iNOS expression were largely suppressed by inhibitors of iNOS (1400 W), nuclear factor-κB (Bay11-7082), actin polymerization (cytochalasin D), caveolae-mediated endocytosis (methyl-β-cyclodextrin, MBCD) and clathrin-mediated endocytosis (monodansylcadaverine, MDC). Electron microscopy revealed that MWCNT was mainly located in vesicular structures in the cytoplasm, and its cellular internalization was reduced by MBCD and MDC. These results suggest that MWCNT is internalized into cells via clathrin- and caveolae-mediated endocytosis, leading to inflammatory reactions including iNOS expression and resulting nitrative DNA damage, which may contribute to carcinogenesis. Highlights: ►Multi-walledcarbon nanotube (MWCNT) caused DNA damage in A549 cells. ►MWCNT formed 8-nitroguanine, a DNA lesion

Black carbon (BC) (as partly burnt black particulate matter) present indoor are deposited on interior surfaces of the indoors (easily visualize over the blades of electric fan/exhausts and over domestic spider webs) are known to be a potential indoor pollution problem. We detect with the help of indoor spider webs the floating BC contains a significant amount of defective multiwalled carbon nanotubes (MWCNTs) possessing room temperature ferromagnetism. Microscopic studies shows a lot of internal and surfacial defects in these indoor-MWCNTs. Electron paramagnetic resonance (EPR) showed the presence of very stable carbon centred radicals in these indoor-MWCNTs. Room temperature ferromagnetism most importantly originated by the presence of a large amount of unpaired spin frustrated carbon centred radicals (trapped in defects, junctions and fractures) which are inadvertently formed during the pyrolysis of carbonaceous materials through routine domestic activities. PMID:24745259

Three-dimensional (3D) electrode microarrays with multi-walledcarbon nanotubes (MWCNTs) reinforced Nafion nanocomposites were prepared for microfluidic biofuel cells. The oxidized MWCNTs (ox-MWCNTs) were prepared using chemical reactions with 60% nitric acid solution with pristine MWCNTs at 120 degrees C for 12 hrs with a nitrogen gas flow environment. Ox-MWCNTs in the range of 1 to 20 wt.% based on the Nafion polymer weight were reinforced to Nafion nanocomposites by solution casting. The micro-porous structure of the ox-MWCNTs reinforced Nafion nanocomposites was prepared by plasma etching for 5 to 20 min. The 10 wt.% ox-MWCNTs reinforced Nafion nanocomposite produced stable micro-porous structures of 3D electrodes by 10 min plasma etching. Micro-scale 3D structures of MWCNTs reinforced Nafion nanocomposites in a diameter range of 47 to 300 μm were prepared by the micro-stencil assisted casting. To characterize the 3D electrode microarrays, the physical geometry and the reinforced MWCNT dispersion in the nanocomposite structure were examined using a scanning electron microscope (SEM) and an optical microscope. Thermal property measurements of the ox-MWCNTs reinforced Nafion nanocomposites with 10 min of plasma etching, and without plasma etching were made. Both showed stable thermal properties over 300 degrees C. The proposed 3D electrode microarray of MWCNT/Nafion nanocomposites with micro-porous structures can be applied to miniaturized fuel cell devices. PMID:25971059

A bioadsorbent of calcium alginate/multi-walledcarbon nanotubes (CA/MWCNTs) composite fiber was fabricated by wet spinning and was characterized. Adsorptions of methylene blue (MB) and methyl orange (MO) ionic dyes onto CA/MWCNT composite fibers were investigated with different MWCNTs content and pH values. The results showed that introduction of MWCNTs of CA/MWCNTs composite fiber could not only sharply increase the adsorption capacity of MO onto bioadsorbent by 3 times, but enhanced the adsorption rate for MB compared to that of native CA fiber. Adsorption kinetics was determined by fitting pseudo-first, second-order and the intra-particle diffusion models to the experimental data, with the second-order model providing the best description of MB and MO adsorption onto CA/MWCNT fibers. The equilibrium adsorption data were analyzed by two widely applied isotherms: Langmuir and Freundlich. The desorption experiments showed the percentage of desorption were found to be 79.7% and 80.2% for MB and MO, respectively. PMID:24751058

We employed a direct one-step solvent-free covalent functionalization of solid fullerene C60 and pristine multi-walledcarbon nanotubes (MWCNTs) with aromatic amines 1-aminopyrene (AP), 2-aminofluorene (AF) and 1,5-diaminonaphthalene (DAN). The reactions were carried out under moderate vacuum, in a wide temperature range of 180-250 °C, during relatively short time of about 2 h. To confirm successful amine attachment, a large number of analytical techniques were used (depending on the nanomaterial functionalized) such as Fourier transform infrared, Raman, X-ray photoelectron, 13C cross-polarization magic angle spinning NMR spectroscopy, thermogravimetric analysis, laser-desorption ionization time-of-flight mass spectrometry, temperature-programmed desorption with mass spectrometric detection, as well as scanning and transmission electron microscopy. The nucleophilic addition of the aromatic amines to C60 molecule was studied theoretically by using density functional theory (PBE GGA functional with Grimme dispersion correction in conjunction with the DNP basis set). In the case of crystalline C60, the solvent-free technique has a limited applicability due to poor diffusion of vaporous aromatic amines into the bulk. Nevertheless, the approach proposed allows for a facile preparation of aromatic amine-functionalized pristine MWCNTs without contamination with other chemical reagents, detergents and solvents, which is especially important for a vast variety of nanotube applications spanning from nanoelectronics to nanomedicine.

The goal of the present work was to test the feasibility of simple, one-step and solvent-free covalent functionalization of pristine multi-walledcarbon nanotubes (MWNTs) and fullerene C60 (as a model system) with amino-substituted crown ethers, namely, 4'-aminobenzo-15-crown-5 and 4'-aminobenzo-1 8-crown-6. The attachment technique proposed is based on thermal instead of chemical activation, and can be considered as ecologically friendly. The suggested covalent binding mechanism is the nucleophilic addition of amino functionalities of crown ethers to the 6,6 bonds of pyracylene units in the case of C60, and to pentagonal (and probably other) defects of similar nature in the case of pristine MWNTs. The hybrids of crown ethers with MWNTs were characterized by means of scanning and transmission electron microscopy, Fourier-transform infrared and Raman spectroscopy, as well as thermogravimetric analysis. The functionalized C60 samples were additionally studied by means of 13C cross-polarization magic angle spinning nuclear magnetic resonance spectroscopy and laser desorption/ionization time-of-flight mass spectrometry. The approach proposed allows for a facile preparation of crown ether-functionalized pristine MWNTs without contamination with other chemical reagents, detergents and solvents, which is especially important for a vast variety of nanotube applications ranging from nanoelectronics to nanomedicine. PMID:27427687

To date, there has not been an agreement on the best methods for the characterisation of multi-walledcarbon nanotube (MWCNT) toxicity. The length of MWCNTs has been identified as a factor in in vitro and in vivo studies, in addition to their purity and biocompatible coating. Another unresolved issue relates to the variable toxicity of MWCNTs on different cell types. The present study addressed the effects of MWCNTs' length on mammalian immune and epithelial cancer cells RAW264.7 and MCF-7, respectively. Our data confirm that MWCNTs induce cytotoxicity in a length- and cell type-dependent manner. Whereas, longer (3 to 14 μm) MWCNTs exert high toxicity, especially to RAW264.7 cells, shorter (1.5 μm) MWCNTs are significantly less cytotoxic. These findings confirm that the degree of biocompatibility of MWCNTs is closely related to their length and that immune cells appear to be more susceptible to damage by MWCNTs. Our study also indicates that MWCNT nanotoxicity should be analysed for various components of cellular response, and cytotoxicity data should be validated by the use of more than one assay system. Results from chromogenic-based assays should be confirmed by trypan blue exclusion. PMID:22748010

We have evaluated tunnel barriers formed in multi-walledcarbon nanotubes (MWNTs) by an Ar atom beam irradiation method and applied the technique to fabricate coupled double quantum dots. The two-terminal resistance of the individual MWNTs was increased owing to local damage caused by the Ar beam irradiation. The temperature dependence of the current through a single barrier suggested two different contributions to its Arrhenius plot, i.e., formed by direct tunneling through the barrier and by thermal activation over the barrier. The height of the formed barriers was estimated. The fabrication technique was used to produce coupled double quantum dots with serially formed triple barriers on a MWNT. The current measured at 1.5 K as a function of two side-gate voltages resulted in a honeycomb-like charge stability diagram, which confirmed the formation of the double dots. The characteristic parameters of the double quantum dots were calculated, and the feasibility of the technique is discussed.

The multi-walledcarbon nanotubes/nickel (MWCNTs/Ni) nanocomposite coatings were prepared on Cu substrate by electro-deposition method in the electrolyte with well-dispersed MWCNTs. Surface morphologies of the composite coatings with protrusion structures were confirmed by scanning electron microscopy. X-ray diffraction, fourier transform infrared spectroscopy, and energy-dispersive x-ray spectrometer were used to characterize the phase structures, functional groups, and elements distribution of the coatings as well as the incorporated MWCNTs. In addition, the effect of MWCNTs percentage on thickness, hardness, wear, and corrosion resistance of the coatings was also investigated. Results indicated that the incorporation of MWCNTs positively affected the hardness of coatings for their strengthening skeletons effect. Meanwhile, the coating with the MWCNTs concentration of 0.2 g/L could achieve the lowest friction coefficient, wear rate as well as the mass loss in the tribological test by a ball-on-disk tribometer. And also, the optimal corrosion resistance with the highest corrosion potential ( E corr) and the lowest corrosion current density ( I corr) of the composite coating was finally proved after the potentiodynamic polarization evaluation, which could promote the potential applications in preparing the functional nanocomposite materials.

In this study, the effect of water magnetization was investigated on the performance of electrophoretic deposition (EPD) of multi-walledcarbon nanotubes (MWCNTs). Magnetization of water was carried out via two different methods including static and dynamic magnetization processes. It has been found that magnetization of water, as the EPD medium, could enhance several characteristics of MWCNT thin films (MWCNT-TFs). Application of magnetized water as solvent in EPD process resulted in higher electrical conductivity of EPD suspension; consequently, required deposition time was reduced and the electrolysis of water, which is known as one of the main disadvantages of water-based EPDs, was controlled to some extent. Surface morphology of MWCNT-TFs was studied via scanning electron microscopy, and notable enhancement was detected in uniformity and density of MWCNT-TF network. Significant improvement was achieved in electrical conductivity (up to 54 % increase in current) of MWCNT-TF by measuring the current versus voltage characteristics of MWCNT-TFs.

Although there is an important set of data showing potential genotoxic effects of nanomaterials (NMs) at the DNA (comet assay) and chromosome (micronucleus test) levels, few studies have been conducted to analyze their potential mutagenic effects at gene level. We have determined the ability of multi-walledcarbon nanotubes (MWCNT, NM401), to induce mutations in the HPRT gene in Chinese hamster lung (V79) fibroblasts. NM401, characterized in the EU NanoGenotox project, were further studied within the EU Framework Programme Seven (FP7) project NANoREG. From the proliferation assay data we selected a dose-range of 0.12 to 12µg/cm(2) At these range we have been able to observe significant cellular uptake of MWCNT by using transmission electron microscopy (TEM), as well as a concentration-dependent induction of intracellular reactive oxygen species. In addition, a clear concentration-dependent increase in the induction of HPRT mutations was also observed. Data support a potential genotoxic/ carcinogenic risk associated with MWCNT exposure. PMID:26774957

Multi-walledcarbon nanotubes (MWCNT) have elicited great interest in biomedical applications due to their extraordinary physical, chemical, and optical properties. Intravenous administration of MWCNT-based medical imaging agents and drugs in animal models was utilized. However, the potential harmful health effects of MWCNT administration in humans have not yet been elucidated. Furthermore, to date, there are no apparent reports regarding the precise mechanisms of translocation of MWCNT into target tissues and organs from blood circulation. This study demonstrates that exposure to MWCNT leads to an increase in cell permeability in human microvascular endothelial cells (HMVEC). The results obtained from this study also showed that the MWCNT-induced rise in endothelial permeability is mediated by reactive oxygen species (ROS) production and actin filament remodeling. In addition, it was found that MWCNT promoted cell migration in HMVEC. Mechanistically, MWCNT exposure elevated the levels of monocyte chemoattractant protein-1 (MCP-1) and intercellular adhesion molecule 1 (ICAM-1) in HMVEC. Taken together, these results provide new insights into the bioreactivity of MWCNT, which may have implications in the biomedical application of MWCNT in vascular targeting, imaging, and drug delivery. The results generated from this study also elucidate the potential adverse effects of MWCNT exposure on humans at the cellular level. PMID:22129238

Multi-walledcarbon nanotubes (MWCNTs) have been reinforced in alumina (Al2O3) matrix to overcome the inherent brittleness of the Al2O3 matrix. In this work, MWCNTs were treated by acid to provide hydrophilicity to hydrophobic MWCNTs, inducing the homogeneous dispersion of MWCNTs in an aqueous solution. Aluminum hydroxide (Al(OH)3) as a Al2O3 precursor was added in the solution with the modified MWCNTs, and then this mixture solution was filtered at room temperature. The prepared powders were calcinated at 800-1000 degrees C to reduce the gas pocket in the matrix by decomposition of Al(OH)3. Then the calcinated powders were formed, and heat-treated. The porous MWCNTs-Al2O3 composites show higher mechanical properties in flexure strength and hardness than the porous Al2O3 without the reinforcement phase, which is attributed to the high mechanical properties of MWCNTs. However, higher MWCNTs contents in the composites decrease the mechanical properties due to the aggregation of MWCNTs in the composites. Therefore, control of the MWCNTs content and its dispersibility in the matrix are key factors to be considered for the fabrication of the porous MWCNT-Al2O3 composites. PMID:22103230

In the present study, a new analytical method has been developed for the simultaneous quantification of 15 organophosphorus pesticides, including some of their metabolites, (disulfoton-sulfoxide, ethoprophos, cadusafos, dimethoate, terbufos, disulfoton, chlorpyrifos-methyl, malaoxon, fenitrothion, pirimiphos-methyl, malathion, chlorpyrifos, terbufos-sulfone, disulfoton-sulfone and fensulfothion) in three different types of commercial cereal-based baby foods. Dispersive solid-phase extraction (dSPE) with multi-walledcarbon nanotubes (MWCNTs) was used together with gas chromatography with nitrogen phosphorus detection. Most favorable conditions involved a previous ultrasound-assisted extraction of the sample with acetonitrile containing formic acid. After evaporation of the extract and redissolution in water, a dSPE procedure was carried out with MWCNTs. The whole method was validated in terms of repeatability, linearity, precision and accuracy and matrix effect was also evaluated. Absolute recoveries were in the range 64-105 % with relative standard deviation values below 7.6 %. Limits of quantification achieved ranged from 0.31 to 5.50 μg/kg, which were lower than the European Union maximum residue limits for pesticide residues in cereal-based baby foods. PMID:22623047

The effect of wet acid oxidation by means of sulfuric/nitric acid mixtures, and high-temperature treatment of commercial arc-discharge synthesized multi-walledcarbon nanotubes (MWCNTs) was studied. In order to analyze the adsorption capacities of differently treated MWCNTs, we employed a multistep method that considers separately different pressure ranges (zones) on the experimentally obtained isotherms. The method is based on simple gas isotherm measurements (N2, CO2, CH4, etc.). Low pressure ranges can be described using Dubinin’s model, while high pressure regimes can be fitted using different models such as BET multilayer and Freundlich equations. This analysis allows to elucidate how different substrate treatments (chemical and thermal) can affect the adsorbate-adsorbent interactions; moreover, theoretical description of adsorbate-adsorbate interactions can be improved if a combination of adsorption mechanisms are used instead of a unique model. The results hereby presented also show that, while MWCNTs are a promising material for storage applications, gas separation applications should carefully consider the effect of wide nanotube size distribution present on samples after activation procedures.

To date, there has not been an agreement on the best methods for the characterisation of multi-walledcarbon nanotube (MWCNT) toxicity. The length of MWCNTs has been identified as a factor in in vitro and in vivo studies, in addition to their purity and biocompatible coating. Another unresolved issue relates to the variable toxicity of MWCNTs on different cell types. The present study addressed the effects of MWCNTs' length on mammalian immune and epithelial cancer cells RAW264.7 and MCF-7, respectively. Our data confirm that MWCNTs induce cytotoxicity in a length- and cell type-dependent manner. Whereas, longer (3 to 14 μm) MWCNTs exert high toxicity, especially to RAW264.7 cells, shorter (1.5 μm) MWCNTs are significantly less cytotoxic. These findings confirm that the degree of biocompatibility of MWCNTs is closely related to their length and that immune cells appear to be more susceptible to damage by MWCNTs. Our study also indicates that MWCNT nanotoxicity should be analysed for various components of cellular response, and cytotoxicity data should be validated by the use of more than one assay system. Results from chromogenic-based assays should be confirmed by trypan blue exclusion.

Relationships between the physical properties of carbon nanotubes (CNTs) and their toxicities have been studied. However, little research has been conducted to investigate the pulmonary and pleural inflammation caused by short-fiber single-walled CNTs (SWCNTs) and multi-walled CNTs (MWCNTs). This study was performed to characterize differences in rat pulmonary and pleural inflammation caused by intratracheal instillation with doses of 0.15 or 1.5mg/kg of either short-sized SWCNTs or MWCNTs. Data from bronchoalveolar lavage fluid analysis, histopathological findings, and transcriptional profiling of rat lungs obtained over a 90-day period indicated that short SWCNTs caused persistent pulmonary inflammation. In addition, the short MWCNTs markedly impacted alveoli immediately after instillation, with the levels of pulmonary inflammation following MWCNT instillation being reduced in a time-dependent manner. MWCNT instillation induced greater levels of pleural inflammation than did short SWCNTs. SWCNTs and MWCNTs translocated in mediastinal lymph nodes were observed, suggesting that SWCNTs and MWCNTs underwent lymphatic drainage to the mediastinal lymph nodes after pleural penetration. Our results suggest that short SWCNTs and MWCNTs induced pulmonary and pleural inflammation and that they might be transported throughout the body after intratracheal instillation. The extent of changes in inflammation differed following SWCNT and MWCNT instillation in a time-dependent manner. PMID:27259835

Excretion of cementum by cementoblasts on the root surface is a process indispensable for the formation of a functional periodontal ligament. This study investigated whether carboxyl group-functionalized multi-walledcarbon nanotubes (MWCNT-COOH) could enhance differentiation and mineralization of mammalian cementoblasts (OCCM-30) and the possible signaling pathway involved in this process. Cementoblasts were incubated with various doses of MWCNT-COOH suspension. Cell viability was detected, and a scanning electron microscopy (SEM) observed both the nanomaterials and the growth of cells cultured with the materials. Alizarin red staining was used to investigate the formation of calcium deposits. Real-time PCR and western blot were used to detect cementoblast differentiation and the underlying mechanisms through the expression of the osteogenic genes and the downstream effectors of the TGF-β/Smad signaling. The results showed that 5 µg/mL MWCNT-COOH had the most obvious effects on promoting differentiation without significant toxicity. Alp, Ocn, Bsp, Opn, Col1 and Runx2 gene expression was up-regulated. Smad2 and Smad3 mRNA was up-regulated, while Smad7 was first down-regulated on Day 3 and later up-regulated on Day 7. The elevated levels of phospho-Smad2/3 were also confirmed by western blot. In sum, the MWCNT-COOH promoted cementoblast differentiation and mineralization, at least partially, through interactions with the TGF-β/Smad pathway. PMID:25648319

The wide application of multi-walledcarbon nanotubes (MWCNT) has raised serious concerns about their safety on human health and the environment. However, the potential harmful effects of MWCNT remain unclear and contradictory. To clarify the potentially toxic effects of MWCNT and to elucidate the associated underlying mechanisms, the effects of MWCNT on human lung adenocarcinoma A549 cells were examined at both the cellular and the protein level. Cytotoxicity and genotoxicity were examined, followed by a proteomic analysis (2-DE coupled with LC-MS/MS) of the cellular response to MWCNT. Our results demonstrate that MWCNT induces cytotoxicity in A549 cells only at relatively high concentrations and longer exposure time. Within a relatively low dosage range (30 µg/ml) and short time period (24 h), MWCNT treatment does not induce significant cytotoxicity, cell cycle changes, apoptosis, or DNA damage. However, at these low doses and times, MWCNT treatment causes significant changes in protein expression. A total of 106 proteins show altered expression at various time points and dosages, and of these, 52 proteins were further identified by MS. Identified proteins are involved in several cellular processes including proliferation, stress, and cellular skeleton organization. In particular, MWCNT treatment causes increases in actin expression. This increase has the potential to contribute to increased migration capacity and may be mediated by reactive oxygen species (ROS). PMID:24454774

In this work, we have enhanced the capability of an e-nose system based on combined optical and electrochemical transduction within a single gas sensor array. The optical part of this e-nose is based on detection of the absorption changes of light emitted from eight light emitting diodes (LEDs) as measured by a CMOS photo-detector. The electrochemical part works by measuring the change in electrical resistivity of the sensing materials upon contact with the sample vapor. Zinc-5,10,15,20-tetra-phenyl-21H,23H-porphyrin (ZnTPP) and multi-walledcarbon nanotube (MWCNT) composite was used as the sensing materials based on its good optoelectronic properties. This sensing layer was characterized by UV-Vis spectroscopy and atomic force microscope and tested with various VOC vapors. Density functional theory (DFT) calculations were performed to investigate the electronic properties and interaction energies between ZnTPP and analyte molecules. It can be clearly seen that this hybrid optical-electrochemical electronic nose system can classify the vapor of different volatile organic compounds. PMID:22966552

The impact of two types of multi-walledcarbon nanotubes (MWCNTs) (12-14 nm) with different content of metallic impurities (purified and unpurified nanotubes) on peroxidation processes, the status of immune cells in healthy volunteers and gene expression combined to pathway analysis was studied in vitro. From the study it was shown that the main mechanism of action for both types of MWCNTs is induction of oxidative stress, the intensity of which is directly related to the amount of metallic impurities. Unpurified MWCNTs produced twice as high levels of oxidation than the purified CNTs inducing thus more intense mitochondrial dysfunction. All the above were also verified by gene expression analysis of 2 different human cellular cultures (lung epithelium and keratinoma cells) and the respective pathway analysis; modulation of genes activating the NFkB pathway is associated to inflammatory responses. This may cause a perturbation in the IL-6 signaling pathway in order to regulate inflammatory processes and compensate for apoptotic changes. A plausible hypothesis for the immunological effects observed in vivo, are considered as the result of the synergistic effect of systemic (mediated by cells of the routes of exposure) and local inflammation (blood cells). PMID:26683310

The acquisition of multidrug resistance poses a serious problem in chemotherapy, and new types of transporters have been actively sought to overcome it. In the present study, poly(ethylene glycol)-conjugated (PEGylated) multi-walledcarbon nanotubes (MWCNTs) were prepared and explored as drug carrier to overcome multidrug resistance. The prepared PEGylated MWCNTs penetrated into mammalian cells without damage plasma membrane, and its accumulation did not affect cell proliferation and cell cycle distribution. More importantly, PEGylated MWCNTs accumulated in the multidrug-resistant cancer cells as efficient as in the sensitive cancer cells. Intracellular translocation of PEGylated MWCNTs was visualized in both multidrug-resistant HepG2-DR cells and sensitive HepG2 cells, as judged by both fluorescent and transmission electron microscopy. PEGylated MWCNTs targeted cancer cells efficiently and multidrug-resistant cells failed to remove the intracellular MWCNTs. However, if used in combination with drugs without conjugation, PEGylated MWCNTs prompted drug efflux in MDR cells by stimulating the ATPase activity of P-glycoprotein. This study suggests that PEGylated MWCNTs can be developed as an efficient drug carrier to conjugate drugs for overcoming multidrug resistance in cancer chemotherapy.

Despite unique and useful properties of multi-walledcarbon nanotubes (MWNTs) such as high strength and a low synthesis cost, their weak antimicrobial property hampers their use as an antimicrobial material. Herein, we demonstrate that the immobilization of nisin, a natural and inexpensive antimicrobial peptide, with poly(ethylene glycol) (PEG1000) as a linker significantly enhanced the antimicrobial and anti-biofilm properties of MWNTs. The MWNT-nisin composite showed up to 7-fold higher antimicrobial property than pristine MWNTs against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Bacillus subtilis. Moreover, the MWNT-nisin composite had a dramatically improved capability to prevent biofilm formation both on a deposited film and in suspension. In particular, the MWNT-nisin deposit film exhibited a 100-fold higher anti-biofilm property than the MWNT deposit film. Further, it has been shown that PEG and nisin are covalently attached to MWNTs with excellent stability against leaching. We envision that our novel MWNT-nisin composite can serve as an effective and economical antimicrobial material.

The current study tests the hypothesis that multi-walledcarbon nanotubes (MWCNT) with different surface chemistries exhibit different bioactivity profiles in vivo. In addition, the study examined the potential contribution of the NLRP3 inflammasome in MWCNT-induced lung pathology. Unmodified (BMWCNT) and MWCNT that were surface functionalised with -COOH (FMWCNT), were instilled into C57BL/6 mice. The mice were then examined for biomarkers of inflammation and injury, as well as examined histologically for development of pulmonary disease as a function of dose and time. Biomarkers for pulmonary inflammation included cytokines, mediators and the presence of inflammatory cells (IL-1β, IL-18, IL-33, cathepsin B and neutrophils) and markers of injury (albumin and lactate dehydrogenase). The results show that surface modification by the addition of the -COOH group to the MWCNT, significantly reduced the bioactivity and pathogenicity. The results of this study also suggest that in vivo pathogenicity of the BMWCNT and FMWCNT correlates with activation of the NLRP3 inflammasome in the lung. PMID:23432020

The development of novel electrode materials with high energy density and long cycling life is critical to realize electrochemical capacitive energy storage for practical applications. In this paper, the hybrids of nickle cobalt sulfide/multi-wallcarbon nanotubes (NiCo2S4/MWCNTs) with different contents of MWCNTs are prepared using a facile one-pot solvothermal reaction. As novel active materials for supercapacitors, the electrochemistry tests show that the hybrid of NiCo2S4/MWCNTs-5 is able to deliver a high specific capacitance of 2080 F g-1 at the current density of 1 A g-1, even superior rate capability of 61% capacitance retention after a 20-fold increase in current densities, when the content of MWCNTs is up to 5%. More importantly, an asymmetric supercapacitor assembled by NiCo2S4/MWCNTs-5 as positive electrode and reduced graphene oxide (rGO) as negative electrode delivers a high energy density of 51.8 Wh Kg-1 at a power density of 865 W kg-1, and 85.7% of its initial capacitance is retained at the current density of 4 A g-1 after 5000 charge-discharge cycles, exhibiting potential prospect for practical applications.

Engineered nanomaterials have been developed for widespread applications due to many highly unique and desirable characteristics. The purpose of this study was to assess pulmonary inflammation and subepicardial arteriolar reactivity in response to multi-walledcarbon nanotube (MWCNT) inhalation and evaluate the time course of vascular alterations. Rats were exposed to MWCNT aerosols producing pulmonary deposition. Pulmonary inflammation via bronchoalveolar lavage and MWCNT translocation from the lungs to systemic organs was evident 24 h post-inhalation. Coronary arterioles were evaluated 24–168 h post-exposure to determine microvascular response to changes in transmural pressure, endothelium-dependent and -independent reactivity. Myogenic responsiveness, vascular smooth muscle reactivity to nitric oxide, and α-adrenergic responses all remained intact. However, a severe impact on endothelium-dependent dilation was observed within 24 h after MWCNT inhalation, a condition which improved, but did not fully return to control after 168 h. In conclusion, results indicate that MWCNT inhalation not only leads to pulmonary inflammation and cytotoxicity at low lung burdens, but also a low level of particle translocation to systemic organs. MWCNT inhalation also leads to impairments of endothelium-dependent dilation in the coronary microcirculation within 24 h, a condition which does not fully dissipate within 168 h. The innovations within the field of nanotechnology, while exciting and novel, can only reach their full potential if toxicity is first properly assessed. PMID:23203034

The growing use of multi-walledcarbon nanotubes (MWCNTs) across industry has increased human exposures. We tested the hypothesis that pulmonary instillation of MWCNT would exacerbate cardiac ischemia/reperfusion (I/R) injury. One day following intratracheal instillation of 1, 10, or 100 μg MWCNT in Sprague-Dawley rats, we used a Langendorff isolated heart model to examine cardiac I/R injury. In the 100 μg MWCNT group we report increased premature ventricular contractions at baseline and increased myocardial infarction. This was associated with increased endothelin-1 (ET-1) release and depression of coronary flow during early reperfusion. We also tested if isolated coronary vascular responses were affected by MWCNT instillation and found trends for enhanced coronary tone, which were dependent on ET-1, cyclooxygenase, thromboxane, and Rho-kinase. We conclude that instillation of MWCNT promoted cardiac injury by depressing coronary flow, invoking vasoconstrictive mechanisms involving ET-1, cyclooxygenase, thromboxane, and Rho-kinase. PMID:23102262

We studied the dispersity of multi-walledcarbon nanotubes (MWNTs) combined with different metal- lic particles (Ni and Fe). An ultrasonic-assisted water-bath dispersion process was used to dis- perse the metal-coated MWNTs in different solutions and the dispersity was measured using an ultraviolet-visible spectrophotometer. The dispersity and morphology of the MWNTs were characterized using field-emission scanning electron microscopy (FE-SEM) together with digital image processing technology. Effects of dispersant type (sodium dodecyl benzene sulfonate (SDBS), oleic acid, and polymer (TNEDIS)) and surfactant dosage on the dispersity of the metal-coated MWNTs were investigated under controlled and uncontrolled temperatures and results were compared with those from the untreated MWNTs. The results showed that the negative effects of temperature on the ultrasonic dispersion process could be eliminated through a temperature-controlled system. Moreover, the TNEDIS, SDBS, and oleic acid were arranged in the descending order of the dispersion effect degree. The untreated MWNTs, Ni-coated MWNTs, and Fe-coated MWNTs were arranged in the descending degree of dispersity order. Since the metal coating makes the MWNTs harder and more fragile, the metal-coated MWNTs are more likely to fracture during the ultrasonic dispersion process. PMID:27451790

High density polyethylene (HDPE)/multi-walledcarbon nanotube (MWCNT) nanocomposites were prepared by melt mixing using twin-screw extrusion. The extruded pellets were compression moulded at 200°C for 5min followed by cooling at different cooling rates (20°C/min and 300°C/min respectively) to produce sheets for characterization. Scanning electron microscopy (SEM) shows that the MWCNTs are uniformly dispersed in the HDPE. At 4 wt% addition of MWCNTs composite modulus increased by over 110% compared with the unfilled HDPE (regardless of the cooling rate). The yield strength of both unfilled and filled HDPE decreased after rapid cooling by about 10% due to a lower crystallinity and imperfect crystallites. The electrical percolation threshold of composites, irrespective of the cooling rate, is between a MWCNT concentration of 1∼2 wt%. Interestingly, the electrical resistivity of the rapidly cooled composite with 2 wt% MWCNTs is lower than that of the slowly cooled composites with the same MWCNT loading. This may be due to the lower crystallinity and smaller crystallites facilitating the formation of conductive pathways. This result may have significant implications for both process control and the tailoring of electrical conductivity in the manufacture of conductive HDPE/MWCNT nanocomposites.

Polymer nanocomposite of multi-walledcarbon nanotubes (MWCNT) nanoparticles incorporated with polylactic acid (PLA) and liquid natural rubber (LNR) as compatibilizer were prepared via melt blending method using the Haake Rheomix internal mixer. In order to obtain the optimal processing parameter, the nanocomposite with 89 wt % of PLA was blended with 10 wt % of LNR and 1 wt % of MWCNTs were mixed with various mixing parameter condition; mixing temperature, mixing speed and mixing time. The optimum processing parameter of the composites was obtained at temperature of 190°C, rotation speed of 90 rpm and mixing time of 14 min. Next, the effect of MWCNTs loading on the tensile properties of nanocomposites was investigated. The nanocomposites were melt blended using the optimal processing parameter with MWCNTs loading of 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5 and 4 wt %. The result showed that the sample with 3.5 wt % of MWCNTs gave higher tensile strength and Young's modulus. The SEM micrographs confirmed the effect of good dispersion of MWCNTs and their interfacial bonding in PLA nanocomposites. However, the elongation at break decreased with increasing the percentage of MWCNTs.

This is the first report on ultrahigh sensitive and selective electrochemical detection of nanomolar concentrations of dopamine (DA) in the presence of ascorbic acid (AA) at a modified electrode fabricated with a new functional nanocomposite, comprising of multi-walledcarbon nanotube (MWNT) grafted silica network (silica NW) and gold nanoparticles (Au NPs) (MWNT-g-silica NW/Au NPs). The fabrication of MWNT-g-silica NW/Au NPs modified electrodes involves two steps: covalent functionaliztion of MWNT with silica NW and deposition of Au NP. Cyclic voltammetry and differential pulse voltammetry experiments were performed for the individual and simultaneous electrochemical detection of DA (in nanomolar concentrations) and AA. Differential pulse voltammograms at ITO/MWNT-g-silica NW/Au NPs modified electrode (ME) revealed that the current response is linear for DA in the concentration range of 0.1 nM-30 nM with a detection limit of 0.1 nM. This is the lowest detection limit reported for DA. A plausible mechanism is presented for the excellent performance of ITO/MWNT-g-silica NW/Au NPs-ME towards nanomolar detection of DA. The results revealed that MWNT, silica NW and Au NPs in ITO/MWNT-g-silica NW/Au NPs-ME synergistically contribute to the ultrasensitivity and selectivity for the electrochemical detection of nanomolar concentrations of DA in the presence of coexisting species. PMID:20098776

In this report, poly (vinyl alcohol) (PVA) composite fibers with high content of multi-walledcarbon nanotubes and graphene oxide (MWCNTs-GO) hybrids were prepared by gel spinning, and were characterized by TGA, DSC, SEM, XL-2 yarn strength tester and electrical conductivity measurement. The total content of MWCNTs-GO hybrids in the PVA composite fibers, which is up to 25 wt%, was confirmed by TGA analysis. The DSC measurement shows that the melting and crystallization peaks decreased after the addition of nano-fillers. This is due to the reason that the motion of PVA chains is completely confined by strong hydrogen bonding interaction between PVA and nano-fillers. After the addtion of GO, the dispersibility of MWCNTs in composite fibers improved slightly. And the tensile strength and Young's modulus increased by 38% and 67%, respectively. This is caused by the increased hydrogen bonding interaction and synergistic effect through hybridization of MWCNTs and GO. More significantly, the electrical conductivity of PVA/MWCNTs/GO composite fibers enhanced by three orders of magnitude with the addition of GO.

Here we report for the first time, a simple hydrothermal approach for the bulk production of highly conductive and transparent graphene nanoribbons (GNRs) using several counter ions from K2SO4, KNO3, KOH and H2SO4 in aqueous media, where, selective intercalation followed by exfoliation gives highly conducting GNRs with over 80% yield. In these experiments, sulfate and nitrate ions act as a co-intercalant along with potassium ions resulting into exfoliation of multi-walledcarbon nanotubes (MWCNTs) in an effective manner. The striking similarity of experimental results in KOH and H2SO4 that demonstrates partially damaged MWCNTs, implies that no individual K+, SO42− ion plays a key role in unwrapping of MWCNTs, rather this process is largely effective in the presence of both cations and anions working in a cooperative manner. The GNRs can be used for preparing conductive 16 kΩsq−1, transparent (82%) and flexible thin films using low cost fabrication method. PMID:24621526

The health risks of inhalation exposure to engineered nanomaterials in the workplace are a major concern in recent years, and hazard assessments of these materials are being conducted. The pulmonary surfactant of lung alveoli is the first biological entity to have contact with airborne nanomaterials in inhaled air. In this study, we retrospectively evaluated the pulmonary surfactant components of rat lungs after a 4-week inhalation exposure to three different nanomaterials: fullerenes, nickel oxide (NiO) nanoparticles and multi-walledcarbon nanotubes (MWCNT), with similar levels of average aerosol concentration (0.13-0.37 mg/m(3)). Bronchoalveolar lavage fluid (BALF) of the rat lungs stored after previous inhalation studies was analyzed, focusing on total protein and the surfactant components, such as phospholipids and surfactant-specific SP-D (surfactant protein D) and the BALF surface tension, which is affected by SP-B and SP-C. Compared with a control group, significant changes in the BALF surface tension and the concentrations of phospholipids, total protein and SP-D were observed in rats exposed to NiO nanoparticles, but not in those exposed to fullerenes. Surface tension and the levels of surfactant phospholipids and proteins were also significantly different in rats exposed to MWCNTs. The concentrations of phospholipids, total protein and SP-D and BALF surface tension were correlated significantly with the polymorphonuclear neutrophil counts in the BALF. These results suggest that pulmonary surfactant components can be used as measures of lung inflammation. PMID:25950198

Multi-walledcarbon nanotube (MWCNT)/polyaniline (PANI)/MnO 2 (MPM) ternary coaxial structures are fabricated as supercapacitor electrodes via a simple wet chemical method. The electrostatic interaction between negative poly(4-styrenesulfonic acid) (PSS) molecules and positive Mn 2+ ions causes the generation of MnO 2 nanostructures on MWCNT surfaces while the introduction of PANI layers with appropriate thickness on MWCNT surfaces facilitates the formation of MWCNT/PANI/MnO 2 ternary coaxial structures. The thickness of PANI coatings is controlled by tuning the aniline/MWCNT ratio. The effect of PANI thickness on the subsequent MnO 2 nanoflakes attachment onto MWCNTs, and the MPM structures is investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and field-emission scanning electron microscopy (FESEM). The results suggest that appropriate thickness of PANI layers is important for building MPM ternary coaxial structures without the agglomeration of MnO 2 nanoflakes. The MPM ternary coaxial structures provide large interaction area between the MnO 2 nanoflakes and electrolyte, and improve the electrochemical utilization of the hydrous MnO 2, and decrease the contact resistance between MnO 2 and PANI layer coated MWCNTs, leading to intriguing electrochemical properties for the applications in supercapacitors such as a specific capacitance of 330 Fg -1 and good cycle stability.

Carbon nanotubes (CNTs) are promising nanomaterials having unique physical and chemical properties, with applications in a variety of fields. In this review, we briefly summarize the intrinsic properties of highly purified multi-walled CNTs (MWCNTs, HTT2800) and their potential hazardous effects on intracellular and extracellular pathways, which alter cellular signaling and impact major cell functions such as differentiation, reactive oxygen species (ROS) production, apoptosis, and autophagy. A recent study suggested that the induction of autophagy by CNTs causes nanotoxicity. Autophagy was recently recognized as a critical cell death pathway, and autophagosome accumulation has been found to be associated with exposure to CNTs. Although autophagy is considered as a cytoprotective process, it is often observed in association with cell death, and the relationship between autophagy and cell death remains unclear. Our recent study suggests that the levels of autophagy-related genes (LC3B) and autophagosome formation are clearly up-regulated, along with an increase in numbers of autophagosome vacuoles. This review highlights the importance of autophagy as an emerging mechanism of CNT toxicity. PMID:25546386

In this study, multi-walledcarbon nanotubes (MWCNT) with selected properties, including pristine MWCNT, hydroxylated MWCNT (H-MWCNT), thin-walled MWCNT with large inner diameter (L-MWCNT), aminated MWCNT, and high-purity MWCNT were investigated for dynamic removal of eight pharmaceuticals and personal care products (PPCP). The removal ratios of different PPCP by the pristine MWCNT followed a decreasing order of triclosan (0.93) > prometryn (0.71) > 4-acetylamino-antipyrine (0.67) > carbendazim (0.65) > caffeine (0.42) > ibuprofen (0.34) > acetaminophen (0.29) at 100 min of filtration. Similar or even higher PPCP removals were obtained for all PPCP as the influent concentration decreased, suggesting potential consistent PPCP removals at environmental PPCP concentrations. The removal ratio of acetaminophen was increased to 0.74 by using H-MWCNT. SRFA (Suwannee River fulvic acid) suppressed PPCP adsorption to MWCNT, to greater extents with increasing SRFA concentrations. The L-MWCNT, despite a large inner diameter of 52 ± 3 nm, did not provide better resistance to the competitive adsorption of SRFA than MWCNT with a small inner diameter of 10 ± 2 nm. Future research will be conducted to minimize the effect of SRFA and facilitate application of MWCNT to the treatment of PPCP-contaminated water. PMID:26845455

Background During production and processing of multi-walledcarbon nanotubes (MWCNTs), they may be inhaled and may enter the pulmonary circulation. It is essential that interactions with involved body fluids like the pulmonary surfactant, the blood and others are investigated, particularly as these interactions could lead to coating of the tubes and may affect their chemical and physical characteristics. The aim of this study was to characterize the possible coatings of different functionalized MWCNTs in a cell free environment. Results To simulate the first contact in the lung, the tubes were coated with pulmonary surfactant and subsequently bound lipids were characterized. The further coating in the blood circulation was simulated by incubating the tubes in blood plasma. MWCNTs were amino (NH2)- and carboxyl (-COOH)-modified, in order to investigate the influence on the bound lipid and protein patterns. It was shown that surfactant lipids bind unspecifically to different functionalized MWCNTs, in contrast to the blood plasma proteins which showed characteristic binding patterns. Patterns of bound surfactant lipids were altered after a subsequent incubation in blood plasma. In addition, it was found that bound plasma protein patterns were altered when MWCNTs were previously coated with pulmonary surfactant. Conclusions A pulmonary surfactant coating and the functionalization of MWCNTs have both the potential to alter the MWCNTs blood plasma protein coating and to determine their properties and behaviour in biological systems. PMID:21159192

Aerosol generation and characterization are critical components in the assessment of the inhalation hazards of engineered nanomaterials (NMs). An extensive review was conducted on aerosol generation and exposure apparatus as part of an international expert workshop convened to discuss the design of an in vitro testing strategy to assess pulmonary toxicity following exposure to aerosolized particles. More specifically, this workshop focused on the design of an in vitro method to predict the development of pulmonary fibrosis in humans following exposure to multi-walledcarbon nanotubes (MWCNTs). Aerosol generators, for dry or liquid particle suspension aerosolization, and exposure chambers, including both commercially available systems and those developed by independent researchers, were evaluated. Additionally, characterization methods that can be used and the time points at which characterization can be conducted in order to interpret in vitro exposure results were assessed. Summarized below is the information presented and discussed regarding the relevance of various aerosol generation and characterization techniques specific to aerosolized MWCNTs exposed to cells cultured at the air-liquid interface (ALI). The generation of MWCNT aerosols relevant to human exposures and their characterization throughout exposure in an ALI system is critical for extrapolation of in vitro results to toxicological outcomes in humans. PMID:27108236

The adsorption behavior of different emerging contaminants (3 chloramphenicols, 7 sulfonamides, and 3 non-antibiotic pharmaceuticals) on five types of multi-walledcarbon nanotubes (MWCNTs), and the underlying factors were studied. Adsorption equilibriums were reached within 12h for all compounds, and well fitted by the Freundlich isotherm model. The adsorption affinity of pharmaceuticals was positively related to the specific surface area of MWCNTs. The solution pH was an important parameter of pharmaceutical adsorption on MWCNTs, due to its impacts on the chemical speciation of pharmaceuticals and the surface electrical property of MWCNTs. The adsorption of ionizable pharmaceuticals decreased in varying degrees with the increased ionic strength. MWCNT-10 was found to be the strongest adsorbent in this study, and the Freundlich constant (KF) values were 353-2814mmol(1-n)L(n)/kg, 571-618mmol(1-n)L(n)/kg, and 317-1522mmol(1-n)L(n)/kg for sulfonamides, chloramphenicols, and non-antibiotic pharmaceuticals, respectively. The different adsorption affinity of sulfonamides might contribute to the different hydrophobic of heterocyclic substituents, while chloramphenicols adsorption was affected by the charge distribution in aromatic rings via substituent effects. PMID:26937870

Highlights: • MWCNT/Pd-ZnO were used for photocatalytic reduction of Hg{sup 2+}. • Photocatalytic reduction of Hg{sup 2+} was dependent on wt% of MWCNT, reaction time, and weight of catalyst. • Catalyst re-use revealed the present photocatalyst remain effective and active after five, cycles. - Abstract: Pd-ZnO nanocatalyst supported on multi-walledcarbon nanotubes was successfully synthesized via a modified sol–gel method, and the prepared photocatalyst was used for the environmental remediation of aqueous Hg(II) via photocatalytic reduction under visible light. The prepared MWCNTs/Pd/ZnO nanocomposite photocatalyst was characterized using X-ray diffraction, Brunauer–Emmett–Teller (BET), transmission electron microscopy, and UV–vis spectra (UV–vis). The results showed that both Pd and ZnO nanoparticles were well dispersed over the MWCNTs, and a uniform nanocomposite was formed. The results also illustrated that Pd doping can eliminate the recombination of electron-hole pairs in the catalyst, and the presence of MWCNTs in ZnO composite can change surface properties to achieve sensitivity to visible light. The results demonstrated that optimum mass ratio of CNT:ZnO:Pd were 0.04:1.0:0.08, which resulted in the exceptional performance of the photocatalyst to reduce about 100% of Hg(II) in a 100 mg L solution within 30 min.

Nano-objects have been investigated for drug delivery, oil detection, contaminant removal, and tribology applications. In some applications, they are subjected to friction and deformation during contact with each other and their surfaces on which they slide. Experimental studies directly comparing local and global deformation are lacking. This research performs nanoindentation (local deformation) and compression tests (global deformation) with a nanoindenter (sharp tip and flat punch, respectively) on molybdenum disulfide (MoS2) multi-walled nanotubes (MWNTs), ~500 nm in diameter. Hardness of the MoS2 nanotube was similar to bulk and does not follow the “smaller is stronger” phenomenon as previously reported for other nano-objects. Tungsten disulfide (WS2) MWNTs, ~300 nm in diameter and carbon nanohorns (CNHs) 80–100 nm in diameter were of interest and also selected for compression studies. These studies aid in understanding the mechanisms involved during global deformation when nano-objects are introduced to reduce friction and wear. For compression, highest loads were required for WS2 nanotubes, then MoS2 nanotubes and CNHs to achieve the same displacement. This was due to the greater number of defects with the MoS2 nanotubes and the flexibility of the CNHs. Repeat compression tests of nano-objects were performed showing a hardening effect for all three nano-objects. PMID:25702922

The measurement of observable electromagnetic phenomena in materials and their derived intrinsic electric material properties are of prime importance in the discovery and development of material systems for electronic and aerospace applications. Nanocomposite materials comprised of metal decorated multi-walledcarbon nanotubes (MWCNTs) were prepared by a facile method and characterized. Metal particles such as silver, platinum and palladium with diameters ranging from less than 5 to over 50 nanometers were distributed randomly on the MWCNTs. The metal-containing MWCNTs were then melt mixed into a polymer matrix and the mixture extruded as ribbons. These extruded ribbons exhibited a moderate to high degree of MWCNT alignment as determined by HRSEM. These ribbons were then fabricated into test specimens while maintaining MWCNT alignment and subsequently characterized for electromagnetic properties at 8-12 GHz. The present study is focused on silver decorated MWCNTs dispersed in an Ultem polyimide matrix. The results of the electromagnetic characterization showed that certain sample configurations exhibited a decoupling of the permittivity and loss factor (?? and ??) indicating that these properties could be tailored within certain limits. The decoupling and independent control of these fundamental electrical material parameters offer a new class of materials with potential applications in electronics, microwave engineering and optics.

The measurement of observable electromagnetic phenomena in materials and their derived intrinsic electrical material properties are of prime importance in the discovery and development of material systems for electronic and aerospace applications. Nanocomposite materials comprised of metal decorated multi-walledcarbon nanotubes (MWCNTs) were prepared by a facile method and characterized. Metal particles such as silver(Ag), platinum(Pt) and palladium(Pd) with diameters ranging from less than 5 to over 50 nanometers were distributed randomly on the MWCNTs. The present study is focused on silver decorated MWCNTs dispersed in a polyimide matrix. The Ag-containing MWCNTs were melt mixed into Ultem(TradeMark) and the mixture extruded as ribbons. The extruded ribbons exhibited a moderate to high degree of MWCNT alignment as determined by HRSEM. These ribbons were then fabricated into test specimens while maintaining MWCNT alignment and subsequently characterized for electrical and electromagnetic properties at 8-12 GHz. The results of the electromagnetic characterization showed that certain sample configurations exhibited a decoupling of the permittivity (epsilon ) and loss factor (epsilon") indicating that these properties could be tailored within certain limits. The decoupling and independent control of these fundamental electrical material parameters offers a new class of materials with potential applications in electronics, microwave engineering and optics.

In this study, experiments were carried out to investigate the use of as-synthesized single-walled (SWCNT), double-walled (DWCNT) and multi-walledcarbon nanotubes (MWCNT) agglomerates for the removal of two antibiotics, Oxytetracycline (OXY) and Ciprofloxacin (CIP) from aqueous solution. The variations of key operating parameters on the removal process were assessed in order to find out the optimum conditions. It includes exposure time, solution pH, temperature, ultrasound assistance and desorption assays. The experimental results revealed that a moderate increase in adsorption was registered between pH 3 and 7 for both antibiotics. The application of ultrasound helped enhancing the removal capacities of OXY for all tested CNTs. For the case of MWCNTs, 1h of ultrasonication increased the adsorption capacity by 44.6%. As for CIP, the ultrasonic treatment did not enhance the overall adsorption, especially for the case of DWCNTS. The Brouers-Sotolongo equation was the best fitting isotherm model. The highest removal capacities were registered using SWCNTS for both antibiotics (724 mg/g for CIP and 554 mg/g for OXY). In addition, ethanol was the solvent that induced the highest desorption percent for the case of CIP (52% for MWCNTs). However, the desorption of OXY was negligible for all solvents (maximum 3.3% for DWCNTs using ethanol). PMID:26024613

An electrochemical DNA sensor for Legionella pneumophila detection was constructed using O2 plasma functionalized multi-walledcarbon nanotube (MWCNT) film as a working electrode (WE). The cyclic voltammetry (CV) results revealed that the electrocatalytic activity of plasma functionalized MWCNT (pf-MWCNT) significantly changed depending on O2 plasma treatment time due to some oxygen containing functional groups on the pf-MWCNT surface. Scanning electron microscope (SEM) images and X-ray photoelectron spectroscopy (XPS) spectra were also presented the changes of their surface morphologies and oxygen composition before and after plasma treatment. From a comparison study, it was found that the pf-MWCNT WEs had higher electrocatalytic activity and more capability of probe DNA immobilization: therefore, electrochemical signal changes by probe DNA immobilization and hybridization on pf-MWCNT WEs were larger than on Au WEs. The pf-MWCNT based DNA sensor was able to detect a concentration range of 10 pM-100 nM of target DNA to detect L. pneumophila.

We have evaluated tunnel barriers formed in multi-walledcarbon nanotubes (MWNTs) by an Ar atom beam irradiation method and applied the technique to fabricate coupled double quantum dots. The two-terminal resistance of the individual MWNTs was increased owing to local damage caused by the Ar beam irradiation. The temperature dependence of the current through a single barrier suggested two different contributions to its Arrhenius plot, i.e., formed by direct tunneling through the barrier and by thermal activation over the barrier. The height of the formed barriers was estimated. The fabrication technique was used to produce coupled double quantum dots with serially formed triple barriers on a MWNT. The current measured at 1.5 K as a function of two side-gate voltages resulted in a honeycomb-like charge stability diagram, which confirmed the formation of the double dots. The characteristic parameters of the double quantum dots were calculated, and the feasibility of the technique is discussed.

Inability of nanomedicine to efficiently home to tumor site still poses great challenge in tumor drug delivery. Inspired by the amplified formation of fibrin in clotting cascade, a self-amplified drug delivery system was developed for tumor photothermal therapy (CMWNTs-PEG) using multi-walledcarbon nanotubes (MWNTs) with favorable photothermal effect as the vector, polyethylene glycol as the shelter, CREKA peptide with special affinity for fibrin as the targeting moiety and NIR illumination as the external power. The self-amplified targeting property was carefully characterized. The in vivo temperature monitoring experiment demonstrated that CMWNTs-PEG could significantly elevate the temperature in the tumor region than its counterpart 24 h post an initial NIR illumination. The in vivo imaging and biodistribution experiment showed IR783-labeled CMWNTs-PEG with illumination could accumulate in tumors tissues about 6.4-fold higher than control group, much stronger than other treatment groups. In vivo distribution experiments revealed Cy3-labeled CMWNTs-PEG could deposit on the wall of tumor vessels, intravascular and extravascular spaces, far more extensive than its counterpart in tumor slices. The pharmacodynamics experiment revealed that after four times of illumination, the CMWNTs-PEG almost totally eradiated the tumor xenografts. Altogether, the self-amplified targeting system CMWNTs-PEG showed strong tumor targeting capacity and powerful photothermal therapeutic efficacy. PMID:26695116

Nano-objects have been investigated for drug delivery, oil detection, contaminant removal, and tribology applications. In some applications, they are subjected to friction and deformation during contact with each other and their surfaces on which they slide. Experimental studies directly comparing local and global deformation are lacking. This research performs nanoindentation (local deformation) and compression tests (global deformation) with a nanoindenter (sharp tip and flat punch, respectively) on molybdenum disulfide (MoS2) multi-walled nanotubes (MWNTs), ~500 nm in diameter. Hardness of the MoS2 nanotube was similar to bulk and does not follow the "smaller is stronger" phenomenon as previously reported for other nano-objects. Tungsten disulfide (WS2) MWNTs, ~300 nm in diameter and carbon nanohorns (CNHs) 80-100 nm in diameter were of interest and also selected for compression studies. These studies aid in understanding the mechanisms involved during global deformation when nano-objects are introduced to reduce friction and wear. For compression, highest loads were required for WS2 nanotubes, then MoS2 nanotubes and CNHs to achieve the same displacement. This was due to the greater number of defects with the MoS2 nanotubes and the flexibility of the CNHs. Repeat compression tests of nano-objects were performed showing a hardening effect for all three nano-objects. PMID:25702922

We report the fabrication of a novel amperometric sensor for tryptophan (Trp) based on a pristine multi-walledcarbon nanotube/graphene oxide (pMWCNT/GO) hybrid obtained through the sonication of pMWCNTs in an aqueous solution of GO. The results of transmission electron microscopy and electrochemical impedance spectroscopy demonstrate the successful formation and the excellent charge transfer ability of the resulting hybrid. Compared with the commonly used acid-treated MWCNTs and GO, the resulting hybrid exhibits better electrocatalytic activity towards the oxidation of Trp, which is attributed to the synergistic effect of MWCNTs and GO. The current-time curve reveals that the catalytic oxidation current is linearly dependent on Trp concentration in the range of 50 nM to 4.25 μM with a detection limit of 8 nM (S/N = 3). In addition, the proposed sensor is successfully employed to detect Trp in the real samples with satisfactory results. PMID:26065906

Two catalysts are synthesized by wet impregnation of multiwalledcarbon nanotubes (MWCNT) with a complex formed between Co(II) ions and the nitrogen-containing molecule 2,4,6-tris(2-pyridyl)-1,3,5-triazine (TPTZ), followed by one or two identical heat treatments in N2 atmosphere at 800 °C for 3 h. Catalysts are fully characterized by FESEM, EDX, BET, XRD, FTIR, TGA, XPS analyses, and electrochemical techniques. The electrocatalytic activity towards oxygen reduction reaction (ORR) of the catalysts in acid conditions is assessed by means of a rotating disk electrode (RDE) apparatus and a specific type of cell equipped with a gas diffusion working electrode (GDE). In both testing approaches, the catalyst heat-treated twice (Co-N/MWCNT-2) exhibits higher electroactivity than the catalyst heat-treated once (Co-N/MWCNT-1). Chronoamperometries both in RDE and GDE cell are also performed, showing less electroactivity decay and better current performance for the catalyst heat-treated twice.

Using Saccharomyces cerevisiae as an experimental model, the potential toxicological effects of oxidized multi-walledcarbon nanotubes (MWCNTs) were investigated following exposure to 0-600mg/L for 24h. Results indicated that MWCNTs (>100mg/L) had adverse effects on the cell proliferation. MWCNTs were clearly visible in lysosome, vacuole, endosome, mitochondria, multivesicular body and localization in the perinuclear region. The uptake kinetics data demonstrated that the maximum MWCNTs content (209.61mg/g) was reached at 3h, and a steady state was reached after 18h. Based on the combined results of transmission electron microscope, endocytosis inhibition experiments and endocytosis-related genes (END3, END6, Sla2 and Rsp5) expression analysis, we elucidated MWCNTs uptake mechanism: (i) via a direct penetration of single MWCNTs; (ii) via endocytosis of single MWCNTs; and (iii) via endocytosis of MWCNTs aggregates. The percentage of apoptosis was significant increased at 600mg/L. The decrease of mitochondrial transmembrane potential and the leakage of cytochrome c shown dose-dependent manners. Interestingly, there was no significant increase of reactive oxygen species (ROS). The apoptosis-related genes (SOD1, SOD2, Yca1, Nma111 and Nuc1) were significant changed. These results obtained in our study demonstrated that oxidized MWCNTs induce Saccharomyces cerevisiae apoptosis via mitochondrial impairment pathway. PMID:27475463

Recent advances in the four-dimensional ultrafast transmission electron microscope (4D-UTEM) with combined spatial and temporal resolutions have made it possible to directly visualize structural dynamics of materials at the atomic level. Herein, we report on our development on a 4D-UTEM which can be operated properly on either the photo-emission or the thermionic mode. We demonstrate its ability to obtain sequences of snapshots with high spatial and temporal resolutions in the study of lattice dynamics of the multi-walledcarbon nanotubes (MWCNTs). This investigation provides an atomic level description of remarkable anisotropic lattice dynamics at the picosecond timescales. Moreover, our UTEM measurements clearly reveal that distinguishable lattice relaxations appear in intra-tubular sheets on an ultrafast timescale of a few picoseconds and after then an evident lattice expansion along the radial direction. These anisotropic behaviors in the MWCNTs are considered arising from the variety of chemical bonding, i.e. the weak van der Waals bonding between the tubular planes and the strong covalent sp2-hybridized bonds in the tubular sheets. PMID:25672762

We report a one-pot synthesis of amphiphilic block copolymer-stabilized PtRu nanoparticle modified multi-walledcarbon nanotubes (MWCNTs) using RuCl(3)·xH(2)O and H(2)PtCl(6)·6H(2)O as ruthenium and platinum sources, and block copolymer poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) as stabilizer agent. PtRu alloyed nanoparticles with an average diameter of 4.6nm are well decorated homogeneously on the exterior surfaces of the MWCNTs. The electrochemical catalytic activity for methanol oxidation of PtRu/MWCNTs and commercial PtRu/C (E-TEK) is comparatively investigated using cyclic voltammetry and chronoamperometry. It is revealed that the PtRu nanoparticle modified MWCNT samples display an enhanced electrochemical catalytic activity than commercial PtRu/C electrode. These results show that PtRu nanoparticles may find applications to fuel cells. PMID:22104276

The optical absorption efficiencies of vertically aligned multi-walled (MW)-carbon nanotube (CNT) ensembles are characterized in the 350-7000 nm wavelength range where CNT site densities > 1 × 10(11) /cm(2) are achieved directly on metallic substrates. The site density directly impacts the optical absorption characteristics, and while high-density arrays of CNTs on electrically insulating and non-metallic substrates have been commonly reported, achieving high site-densities on metals has been challenging and remains an area of active research. These absorber ensembles are ultra-thin (<10 μm) and yet they still exhibit a reflectance as low as ∼0.02%, which is 100 times lower than the reference; these characteristics make them potentially attractive for high-sensitivity and high-speed thermal detectors. In addition, the use of a plasma-enhanced chemical vapor deposition process for the synthesis of the absorbers increases the portfolio of materials that can be integrated with such absorbers due to the potential for reduced synthesis temperatures. The remarkable ruggedness of the absorbers is also demonstrated as they are exposed to high temperatures in an oxidizing ambient environment, making them well-suited for extreme thermal environments encountered in the field, potentially for solar cell applications. Finally, a phenomenological model enables the determinatiom of the extinction coefficients in these nanostructures and the results compare well with experiment. PMID:23233398

The aim of this work was to evaluate significant factors affecting the thiamethoxam adsorption efficiency using oxidized multi-walledcarbon nanotubes (MWCNTs) as adsorbents. Five factors (initial solution concentration of thiamethoxam in water, temperature, solution pH, MWCNTs weight and contact time) were investigated using 2V(5-1) fractional factorial design. The obtained linear model was statistically tested using analysis of variance (ANOVA) and the analysis of residuals was used to investigate the model validity. It was observed that the factors and their second-order interactions affecting the thiamethoxam removal can be divided into three groups: very important, moderately important and insignificant ones. The initial solution concentration was found to be the most influencing parameter on thiamethoxam adsorption from water. Optimization of the factors levels was carried out by minimizing those parameters which are usually critical in real life: the temperature (energy), contact time (money) and weight of MWCNTs (potential health hazard), in order to maximize the adsorbed amount of the pollutant. The results of maximal adsorbed thiamethoxam amount in both real and optimized experiments indicate that among minimized parameters the adsorption time is one that makes the largest difference. The results of this study indicate that fractional factorial design is very useful tool for screening the higher number of parameters and reducing the number of adsorption experiments. PMID:26151482

Nano-objects have been investigated for drug delivery, oil detection, contaminant removal, and tribology applications. In some applications, they are subjected to friction and deformation during contact with each other and their surfaces on which they slide. Experimental studies directly comparing local and global deformation are lacking. This research performs nanoindentation (local deformation) and compression tests (global deformation) with a nanoindenter (sharp tip and flat punch, respectively) on molybdenum disulfide (MoS2) multi-walled nanotubes (MWNTs), ~500 nm in diameter. Hardness of the MoS2 nanotube was similar to bulk and does not follow the ``smaller is stronger'' phenomenon as previously reported for other nano-objects. Tungsten disulfide (WS2) MWNTs, ~300 nm in diameter and carbon nanohorns (CNHs) 80-100 nm in diameter were of interest and also selected for compression studies. These studies aid in understanding the mechanisms involved during global deformation when nano-objects are introduced to reduce friction and wear. For compression, highest loads were required for WS2 nanotubes, then MoS2 nanotubes and CNHs to achieve the same displacement. This was due to the greater number of defects with the MoS2 nanotubes and the flexibility of the CNHs. Repeat compression tests of nano-objects were performed showing a hardening effect for all three nano-objects.

Multi-walledcarbon nanotubes synthesized using fluidized bed chemical vapor deposition technique were fluorinated sequentially to prepare a series of CFx battery electrodes. Primary battery performance was tested using CFx as a cathode against Li. Fully fluorinated MWNTs showed capacity exceeding 815 mAh g-1 while partially fluorinated samples showed systematically lowered capacity with decreasing x (in CFx). However, fully fluorinated MWCNTs showed distinctly low rechargeable capacity compared to the subfluorinated samples when used as an anode against Li. Mildly fluorinated MWNTs show high capacity and better stability during charge-discharge cycles. High concentrations of fluorine seem to affect capacity retention due to the increased defect densities and reduced electronic conduction. These defects of nanotubes will provide additional pathways for lithium ions to diffuse within the core of the fluorinated structure and to access the electrochemically active C-F sites. XRD, XPS, and Raman spectroscopy were utilized to characterize the samples. Finally the electrochemical performance of fluorinated MWNTs was compared with that of Natural Chinese Graphite (NCG).

The multi-walledcarbon nano-tubes (MWCNT) were magnetized with iron oxide nanoparticles and were characterized by SEM and EDX analyses. These magnetized MWCNT (Mag-CNT) were used as sorbent in dispersive solid phase extraction (DSPE) mode to extract nerve agents and their markers. Mag-CNT were dispersed in water and collected with the help of an external magnet. From Mag-CNT, the adsorbed analytes were eluted and analyzed by GC-FPD in phosphorus mode. DSPE was found to be advantageous over conventional solid phase extraction (SPE) in terms of operational simplicity, speed, handling of large sample volume and recoveries. Extraction parameters such as eluting solvent, sorbent amount, pH and salinity of aqueous samples were optimized. Optimized extraction conditions included 40 mg of Mag-CNT as sorbent, chloroform as eluent, pH 3-11 and salinity 20%. Under the optimized conditions, recoveries from distilled water ranged from 60 to 96% and were comparable in tap and muddy water. Limits of quantification and limits of detection of 0.15 ng/ml and 0.05 ng/ml, respectively, were achieved. Superiority of Mag-CNT over conventional C(18) SPE was also established. PMID:22063538

Filament condition during hot-wire chemical vapor deposition conditions of multi-walledcarbon nanotubes is a major concern for a stable deposition process. We report on the novel application of electron backscatter diffraction to characterize the carburization of tungsten filaments. During the synthesis, the W-filaments transform to W2C and WC. W-carbide growth followed a parabolic behavior corresponding to the diffusion of C as the rate-determining step. The grain size of W, W2C, and WC increases with longer exposure time and increasing filament temperature. The grain size of the recrystallizing W-core and W2C phase grows from the perimeter inwardly and this phenomenon is enhanced at filament temperatures in excess of 1,400°C. Cracks appear at filament temperatures >1,600°C, accompanied by a reduction in the filament operational lifetime. The increase of the W2C and recrystallized W-core grain size from the perimeter inwardly is ascribed to a thermal gradient within the filament, which in turn influences the hardness measurements and crack formation. PMID:24423105

Polyetherimide/Multiwall carbon nanotube (MWNTs) nanocomposites containing as-received and modified (COOH-MWNT) carbon nanotubes were prepared through melt process in extruder and then compression molded. Thermal properties of the composites were characterized by thermo-gravimetric analysis (TGA). Field emission scanning electron microscopy (FESEM) images showed that the MWNTs were well dispersed and formed an intimate contact with the polymer matrix without any agglomeration. However the incorporation of modified carbon nanotubes formed fascinating, highly crosslinked, and compact network structure throughout the polymer matrix. This showed the increased adhesion of PEI with modified MWNTs. Scanning electron microscopy (SEM) also showed high degree of dispersion of modified MWNTs along with broken ends. Dynamic mechanical analysis (DMA) results showed a marginal increase in storage modulus (E') and glass transition temperature (T(g)) with the addition of MWNTs. Increase in tensile strength and impact strength of composites confirmed the use the MWNTs as possible reinforcement agent. Both thermal and electrical conductivity of composites increased, but effect is more pronounced on modification due to formation of network of carbon nanotubes. Addition of acrylic elastomer to developed PEI/MWNTs (modified) nanocomposites resulted in the further increase in thermal and electrical properties due to the formation of additional bond between MWNTs and acrylic elastomers at the interface. All the results presented are well corroborated by SEM and FESEM studies. PMID:19452959

This paper presents a number of factors which have been found to be important to the growth of carbon nanotubes and nanofibres by plasma enhanced chemical vapour deposition. The effect of the electric field in a plasma discharge on nanotube growth is investigated and shown to be important in achieving nanotube alignment. The use of a plasma discharge also enables deposition to take place at lower temperatures, facilitating the use of substrates which would otherwise be damaged. The effect of varying the ratio of carbon feedstock gas to etchant gas is investigated and the ratio is shown to be important for controlling the shape of deposited nanostructures. The effects of varying plasma power are investigated, showing that greater plasma power results in a lower growth rate. Higher levels of plasma power are also shown to cause the sidewalls of deposited carbon nanotubes to be etched. Finally, the growth rate of carbon nanotubes and nanofibres is shown to depend upon the strength of the local electric field. It is proposed that a higher field causes greater ionization within the plasma, which results in a higher growth rate. This is borne out by comparing simulation results with experimental observations.

Carbon nanotubes previously grown on silicon have extremely low reflectance, making them a good candidate for stray light suppression. Silicon, however, is not a good structural material for stray light components such as tubes, stops, and baffles. Titanium is a good structural material and can tolerate the 700 C nanotube growth process. The ability to grow carbon nanotubes on a titanium substrate that are ten times blacker than the current NASA state-of-the-art paints in the visible to near infrared spectra has been achieved. This innovation will allow significant improvement of stray light performance in scientific instruments or any other optical system. This innovation is a refinement of the utilization of multiwalled carbon nano tubes for stray light suppression in spaceflight instruments. The innovation is a process to make the surface darker and improve the adhesion to the substrate, improving robustness for spaceflight use. Bright objects such as clouds or ice scatter light off of instrument structures and components and make it difficult to see dim objects in Earth observations. A darker material to suppress this stray light has multiple benefits to these observations, including enabling scientific observations not currently possible, increasing observational efficiencies in high-contrast scenes, and simplifying instruments and lowering their cost by utilizing fewer stray light components and achieving equivalent performance. The prior art was to use commercially available black paint, which resulted in approximately 4% of the light being reflected (hemispherical reflectance or total integrated scatter, or TIS). Use of multiwalled carbon nanotubes on titanium components such as baffles, entrance aperture, tubes, and stops, can decrease this scattered light by a factor of ten per bounce over the 200-nm to 2,500-nm wavelength range. This can improve system stray light performance by orders of magnitude. The purpose of the innovation is to provide an enhanced

Three types of multiwall carbon nanotubes, one non-functionalized tubes and two functionalized with polar (amino and carboxyl) groups, were used as fillers in a polypropylene resin to develop nanocomposites with improved thermal conductivity. In particular, formulations containing up to 5% in volume of carbon nanotubes, prepared by melt blending, were analyzed in terms of dynamic rheological behavior of melts and thermal conductivity. The former can give information related to the build-up of internal network structures and to the level of dispersion of the fillers. Taking into account that the properties of nanocomposites are strictly related to these aspects, the enhancement of thermal conductivity with respect to the pristine matrix are discussed as a function of the filler content, dispersion of the filler and presence of internal structures.

Experimental data on the stress-strain behavior of a polymer multiwall carbon nanotube (MWCNT) yarn composite are used to motivate an initial study in multi-scale modeling of strength and stiffness. Atomistic and continuum length scale modeling methods are outlined to illustrate the range of parameters required to accurately model behavior. The carbon nanotubes yarns are four-ply, twisted, and combined with an elastomer to form a single-layer, unidirectional composite. Due to this textile structure, the yarn is a complicated system of unique geometric relationships subjected to combined loads. Experimental data illustrate the local failure modes induced by static, tensile tests. Key structure-property relationships are highlighted at each length scale indicating opportunities for parametric studies to assist the selection of advantageous material development and manufacturing methods.

Metal-catalyzed carbon nanotubes are highly sought for a diverse range of applications that include nanoelectronics, battery electrode material, catalysis, hydrogen storage media and reinforcing agents in polymer composites. These latter applications will require vast quantities of nanotubes at competitive prices to be economically feasible. Moreover, reinforcing applications may not require ultrahigh purity nanotubes. Indeed, functionalization of nanotubes to facilitate interfacial bonding within composites will naturally introduce defects into the tube walls, lessening their tensile strength. Current methods of aerosol synthesis of carbon nanotubes include laser ablation of composite targets of carbon and catalyst metal within high temperature furnaces and decomposition of a organometallics in hydrocarbons mixtures within a tube furnace. Common to each approach is the generation of particles in the presence of the reactive hydrocarbon species at elevated temperatures. In the laser-ablation approach, the situation is even more dynamic in that particles and nanotubes are borne during the transient cooling phase of the laser-induced plasma for which the temperature far exceeds that of the surrounding hot gases within the furnace process tube. A shared limitation is that more efficient methods of nanoparticle synthesis are not readily incorporated into these approaches. In contrast, combustion can quite naturally create nanomaterials such as carbon black. Flame synthesis is well known for its commercial scalability and energy efficiency. However, flames do present a complex chemical environment with steep gradients in temperature and species concentrations. Moreover, reaction times are limited within buoyant driven flows to tens of milliseconds. Therein microgravity can greatly lessen temperature and spatial gradients while allowing independent control of flame residence times. In preparation for defining the microgravity experiments, the work presented here focuses

We investigated the electrical conductivity (sigma) and mechanical property of polyvinylchloride/carbon nanotube composites as a function of the CNT content and processing time during a solid-state process of high speed vibration mixing (HSVM) and high energy ball milling (HEBM). Both processes were suggested to avoid high temperatures, solvents, chemical modification of carbon nanotubes. In this study, the percolation threshold (phi(c)) for electrical conduction is about 1 wt% CNT with a sigma value of 0.21 S/m, and the electrical conductivity is higher value than that reported by other researchers from melt mixing process or obtained from the other solid-state processes. We found that the dispersion of CNTs and morphology change from CNT breaking are closely related to sigma. Especially, a large morphology change in the CNTs was occurred at the specific processing time, and a significant decrease in the electrical conductivity of polyvinylchloride/carbon nanotube composite occurred in this condition. A meaningful increase of electrical properties and mechanical property is observed in the sample with about 1-2 wt% CNT contents sintered at 200 degrees C after the milling for 20 min by HEBM process. Our study indicates the proper process condition required to improve sigma of PVC/CNT composites. PMID:24245322

We have studied the formation of topological defects in liquid crystal (LC) matrices induced by multiwalled carbon nanotubes (MWCNTs) and external electric fields. The defects are ascribable to a distortion of the LC molecular director in proximity of the MWCNT surface. The system is analyzed macroscopically using spectroscopic variable angle ellipsometry. Concurrently, confocal micro-Raman spectroscopy is used to study the system state at the microscale. This allows to acquire a three-dimensional, spatially-resolved map of the topological defect, determining scale length variations and orientation topography of the LC molecules around the MWCNT. PMID:27410863

Functionalized carbon nanotubes (f-CNTs) have been widely used in bio-medicine as drug carriers, bio-sensors, imaging agents and tissue engineering additives, which demands better understanding of their in vivo behavior because of the increasing exposure potential to humans. However, there are limited studies to investigate the in vivo biodistribution and elimination of f-CNTs. In this study, superparamagnetic iron oxides (SPIOs) were used to label oxidized multiwalled carbon nanotubes (o-MWCNTs) for in vivo distribution study of o-MWCNTs by magnetic resonance imaging (MRI). SPIO labeled o-MWCNTs (((SPIO))o-MWCNTs) were prepared by a hydrothermal reaction process, and characterized by TEM, XRD and magnetometer. ((SPIO))o-MWCNTs exhibited superparamagnetic property, excellent biocompatibility and stability. The intravenously injected ((SPIO))o-MWCNTs were observed in liver, kidney and spleen, while the subcutaneously injected ((SPIO))o-MWCNTs could be only detected in sub mucosa. Most of the intravenously injected ((SPIO))o-MWCNTs could be eliminated from liver, spleen, kidney and sub mucosa on 4 d post injection (P.I.). However, the residual o-MWCNTs could induce 30-40% MRI signal-to-noise ratio changes in these tissues even on 30 d P.I. This in vivo biodistribution and elimination information of o-MWCNTs will greatly facilitate the application of f-CNT based nanoproducts in biomedicine. In addition, the magnetic labeling method provides an approach to investigate the in vivo biodistribution and clearance of other nanomaterials. PMID:25409786

Phase shift tapping mode scanning force microscopy (TMSFM) has evolved into a very powerful technique for the nanoscale surface characterization of compositional variations in heterogeneous samples. Phase shift signal measures the difference between the phase angle of the excitation signal and the phase angle of the cantilever response. The signal correlates to the tip-sample inelastic interactions, identifying the different chemical and/or physical property of surfaces. In general, the resolution and quality of scanning probe microscopic images are highly dependent on the size of the scanning probe tip. In improving AFM tip technology, we recently developed a technique for sharpening the tip of a multi-walledcarbon nanotube (CNT) AFM tip, reducing the radius of curvature of the CNT tip to less than 5 nm while still maintaining the inherent stability of multi-walled CNT tips. Herein we report the use of sharpened (CNT) AFM tips for phase-imaging of polymer hybrids, a precursor for generating nanoporous low-k dielectrics for on-chip interconnect applications. Using sharpened CNT tips, we obtained phase-contrast images having domains less than 10 nm. In contrast, conventional Si tips and unsharpened CNT tips (radius greater than 15 nm) were not able to resolve the nanoscale domains in the polymer hybrid films. C1early, the size of the CNT tip contributes significantly to the resolution of phase-contrast imaging. In addition, a study on the nonlinear tapping dynamics of the multi-walled CNT tip indicates that the multi-walled CNT tip is immune to conventional imaging instabilities related to the coexistence of attractive and repulsive tapping regimes. This factor may also contribute to the phase-contrast image quality of multi-walled CNT AFM tips. This presentation will also offer data in support of the stability of the CNT tip for phase shift TMSFM.

Direct electrochemistry and activity of myoglobin (Mb) immobilized on carbon nanotube (CNT) forest electrodes were investigated by probing mainly its electrocatalytical response towards oxygen. The protein was anchored on the CNT electrodes through carbodiimide coupling, which was shown to provide long term stability. The electrochemical response was monitored as a function of oxygen concentration and pH. Conformational changes together with the consequent loss of oxygen affinity were recorded at low pH, which delimits the operative range of the Mb/CNT electrodes for sensing purposes. In general, it can be concluded that CNT forests constitute suitable platforms for Mb attachment without compromising the protein bioactivity and by keeping at the same time the direct electron exchange with the heme core. All these characteristics confer to the protein modified CNT system promising properties for the implementation of (bio)sensor devices with impact in the clinical and environmental field. PMID:19908505

The purpose of this paper is to investigate the effect of multiwalled carbon nanotubes (MWCNTs)/magnesium (Mg) hybrid filler in polyurethane (PU) foams with different weight percentages (0.5 wt.% to 3.0 wt.%). The PU/MWCNTs/Mg foam composites were formed by reaction of based palm oil polyol (POP) with methylene diphenyl diisocyanate (MDI) with ratio 1:1.1 by weight. The foam properties were evaluated in density, morphology and compressive strength. The addition of 2.5 wt.% hybrid filler showed the higher density in 59.72 kg/m3 and thus contribute to the highest compressive strength at 1.76 MPa. The morphology show cell in closed structure and addition hybrid filler showed uneven structure.

Nanohydroxyapatite (nHAp) is an emergent bioceramic that shows similar chemical and crystallographic properties as the mineral phase present in bone. However, nHAp presents low fracture toughness and tensile strength, limiting its application in bone tissue engineering. Conversely, multi-walledcarbon nanotubes (MWCNTs) have been widely used for composite applications due to their excellent mechanical and physicochemical properties, although their hydrophobicity usually impairs some applications. To improve MWCNT wettability, oxygen plasma etching has been applied to promote MWCNT exfoliation and oxidation and to produce graphene oxide (GO) at the end of the tips. Here, we prepared a series of nHAp/MWCNT-GO nanocomposites aimed at producing materials that combine similar bone characteristics (nHAp) with high mechanical strength (MWCNT-GO). After MWCNT production and functionalization to produce MWCNT-GO, ultrasonic irradiation was employed to precipitate nHAp onto the MWCNT-GO scaffolds (at 1-3 wt%). We employed various techniques to characterize the nanocomposites, including transmission electron microscopy (TEM), Raman spectroscopy, thermogravimetry, and gas adsorption (the Brunauer-Emmett-Teller method). We used simulated body fluid to evaluate their bioactivity and human osteoblasts (bone-forming cells) to evaluate cytocompatibility. We also investigated their bactericidal effect against Staphylococcus aureus and Escherichia coli. TEM analysis revealed homogeneous distributions of nHAp crystal grains along the MWCNT-GO surfaces. All nanocomposites were proved to be bioactive, since carbonated nHAp was found after 21 days in simulated body fluid. All nanocomposites showed potential for biomedical applications with no cytotoxicity toward osteoblasts and impressively demonstrated a bactericidal effect without the use of antibiotics. All of the aforementioned properties make these materials very attractive for bone tissue engineering applications, either as a

Multi-walledcarbon nanocoil (MWCNC) is a carbon nanotube (CNT) with helical shape. We have synthesized MWCNCs and MWCNTs hybrid by chemical vapor deposition (CVD). MWCNCs are considered to be a potential material in nanodevices, such as electromagnetic wave absorbers and field emitters. It is very important to take into account the purity of MWCNCs. In this study, we aimed to improve the composition ratio of MWCNCs to MWCNTs by changing catalyst preparation and CVD conditions. As a catalyst, Fe2O3/zeolite was prepared by dissolving Fe2O3 fine powder and Y-type zeolite (catalyst support material) in ethanol with an Fe density of 0.5wt.% and with a zeolite density of 3.5wt.%. The catalyst-coated Si substrate was transferred immediately onto a hotplate and was heated at 80°C for 5 min. Similarly, Fe2O3/Al2O3, Co/zeolite/Al2O3, Co/zeolite, and Co/Al2O3 were prepared. The effect of the difference of the composite catalysts on synthesis of MWCNCs was considered. The CVD reactor was heated in a tubular furnace to 660-790°C in a nitrogen atmosphere at a flow rate of 1000 ml/min. Subsequently, acetylene was mixed with nitrogen at a flow rate ratio of C2H2/N2 = 0.02-0.1. The reaction was kept under these conditions for 10 min. MWCNTs and MWCNCs were well grown by the catalysts of Co/zeolite and Co/Al2O3. The composition ratio of MWCNCs to MWCNTs was increased by using a combination of zeolite and Al2O3. The highest composition ratio of MWCNCs to MWCNTs was 12%.

In spite of the increasing concerns about the fate of pharmaceuticals and personal care products (PPCPs) and the nanomaterial pollution in aquatic ecosystem, the effects of carbon nanotubes on the photochemical transformation of PPCPs are less considered. In this study, the photochemical production of reactive oxygen species (ROS) were examined in colloidal dispersions of hydroxylated multi-walledcarbon nanotubes (MWNT-OH) under simulated solar irradiation using a Xenon lamp. Two kinds of ROS, (1)O2 and OH, were confirmed by their molecular probes, furfuryl alcohol (FFA) and p-chlorobenzoic acid (PCBA). The steady-state concentrations of (1)O2 and OH were calculated as 1.30×10(-14) M and 5.02×10(-16) M, respectively. The effects of MWNT-OH on photodegradation of atenolol (ATL) were investigated in the presence of natural water components, i.e., dissolved organic matters (DOMs), nitrate (NO3(-)) and ferric ions (Fe(3+)). Photoproducts of atenolol were identified by solid phase extraction-liquid chromatography-mass spectrometry (SPE-LC-MS) analysis techniques. Three potential photochemical pathways of atenolol, including the hydroxylation on aromatic ring, the loss of amide group and the cleavage of ether oxygen bond as well as di-polymerization of reaction intermediates were tentatively proposed. Using the radical quenching method, reaction with OH was determined as the major photolysis pathway of atenolol in irradiated MWNT-OH suspensions. These findings of the production of ROS and their effects on the photodegradation of organic contaminants provided useful information for assessing environmental risk of MWNT-OH. PMID:23816450

Pharmaceutical micropollutants fall in the category of "emerging contaminants" in water because of their prevalence and persistence in the aqueous environment, and because of a poor understanding of their low-dose exposure effects on human and animal populations. In this study, photo-regenerable multiwalled carbon nanotube membranes with variable water permeabilities were produced by embedding hierarchical TiO2 structures (having porous, spherical morphology) onto a pre-deposited bed of multi-walledcarbon nanotubes (MWNTs) using a modified sol-gel technique. These MWNT-TiO2 composites and their constituent materials were characterized by analytical electron microscopy, surface charge measurement, thermogravimetric analysis, and hydrophobicity determination. The adsorption removal potential of MWNT-TiO2 membranes was demonstrated for three representative pharmaceuticals: acetaminophen, carbamazepine and ibuprofen. The peak initial removal percentages of the pharmaceuticals by the MWNT-TiO2 membranes were 80%, 45%, and 24% for carbamazepine, ibuprofen, and acetaminophen, respectively. The ability of the membranes to be regenerated, once they were saturated with the pharmaceutical compounds, was verified by repeating the adsorption removal experiment on the same membranes after exposure to UV light at 254 nm. Peak removal efficiencies after regeneration were 55%, 32%, and 19% for carbamazepine, ibuprofen, and acetaminophen, respectively, indicating some loss in sorptive capacity upon regeneration. Furthermore, the effect of pH on adsorption of ibuprofen, the pharmaceutical that attained the highest mass loading on the sorbent at equilibrium saturation, was studied and its mechanism of adsorption was proposed at pH below pKa. PMID:23811952

Nanohydroxyapatite (nHAp) is an emergent bioceramic that shows similar chemical and crystallographic properties as the mineral phase present in bone. However, nHAp presents low fracture toughness and tensile strength, limiting its application in bone tissue engineering. Conversely, multi-walledcarbon nanotubes (MWCNTs) have been widely used for composite applications due to their excellent mechanical and physicochemical properties, although their hydrophobicity usually impairs some applications. To improve MWCNT wettability, oxygen plasma etching has been applied to promote MWCNT exfoliation and oxidation and to produce graphene oxide (GO) at the end of the tips. Here, we prepared a series of nHAp/MWCNT-GO nanocomposites aimed at producing materials that combine similar bone characteristics (nHAp) with high mechanical strength (MWCNT-GO). After MWCNT production and functionalization to produce MWCNT-GO, ultrasonic irradiation was employed to precipitate nHAp onto the MWCNT-GO scaffolds (at 1–3 wt%). We employed various techniques to characterize the nanocomposites, including transmission electron microscopy (TEM), Raman spectroscopy, thermogravimetry, and gas adsorption (the Brunauer–Emmett–Teller method). We used simulated body fluid to evaluate their bioactivity and human osteoblasts (bone-forming cells) to evaluate cytocompatibility. We also investigated their bactericidal effect against Staphylococcus aureus and Escherichia coli. TEM analysis revealed homogeneous distributions of nHAp crystal grains along the MWCNT-GO surfaces. All nanocomposites were proved to be bioactive, since carbonated nHAp was found after 21 days in simulated body fluid. All nanocomposites showed potential for biomedical applications with no cytotoxicity toward osteoblasts and impressively demonstrated a bactericidal effect without the use of antibiotics. All of the aforementioned properties make these materials very attractive for bone tissue engineering applications, either as a

Carbon nanotubes (CNTs) are widely explored for biomedical applications, but there is very limited information regarding their in vivo biodistribution and biocompatibility. Here, we report the in vivo biodistribution and long-term effects of functionalized multi-walledcarbon nanotubes (MWCNTs) in developing zebrafish. The fluorescent-labeled MWCNTs were introduced into zebrafish embryos at 1-cell stage and at 72 h post fertilization through microinjection. After single injection, both acute and long-term interactions between zebrafish and functionalized MWCNTs were studied. The injected FITC-BSA-MWCNTs (at 1-cell stage) were allocated to all blastoderm cells of the embryos through proliferation, and were distinctively excluded from the yolk cell. When introduced into the circulation system, FITC-BSA-MWCNTs moved easily in the compartments and finally were cleaned out by the body at 96 h after the loading. At early stages, the treated zebrafish embryos generated immune response by accumulating circulating white blood cells at the trunk region. Under transmission electron microscope, many lysosome-like vesicles were observed in the blastoderm cells of the treated embryos. The zebrafish loaded with MWCNTs had normal primordial germ cells at early stage and produced second generation later on. However, the larvae of the second generation had obviously lower survival rates as compared to the untreated groups, suggesting a negative effect on the reproduction potential. These results suggest that extensive purification and functionalization processes can help improve the biocompatibility of CNTs. This study also indicates that purified CNTs may have long-term toxicity effects when they were delivered into the body.

A novel and highly sensitive electrochemiluminescence (ECL) biosensing system was designed and developed for individual detection of different organophosphorous pesticides (OPs) in food samples. Bimetallic Pt-Au nanoparticles were electrodeposited on multi-walledcarbon nanotubes (MWNTs)-modified glass carbon electrode (GCE) to increase the surface area of electrode and ECL signals of luminol. Biocomposites of enzymes from acetylcholinesterase and choline oxidase (AChE and ChOx) were immobilized onto the electrode surface to produce massive hydrogen peroxides (H2O2), thus amplifying ECL signals. Based on the dual-amplification effects of nanoparticles and H2O2 produced by enzymatic reactions, the proposed biosensor exhibits highly sensitivity. The proposed biosensing approach was then used for detecting OPs by inhibition of OPs on AChE. Under optimized experimental conditions, the ECL intensity decreased accordingly with the increase in concentration of OPs, and the inhibition rates of OPs were proportional to their concentrations in the range of 0.1-50nmolL(-1) for malathion, methyl parathion and chlorpyrifos, with detection limit of 0.16nmolL(-1), 0.09nmolL(-1) and 0.08nmolL(-1), respectively. The linearity range of the biosensor for pesticide dufulin varied from 50 to 500nmolL(-1), with the detection limit of 29.7nmolL(-1). The resulting biosensor was further validated by assessment of OPs residues in cabbage, which showed a fine applicability for the detection of OPs in the realistic sample. PMID:27343588

A novel electrode fabrication technique involving a manual scribing action of vertically aligned silicon coated multiwall carbon nanotubes (VASCNTs) on a copper foil have been developed as a viable approach to Li-ion battery electrodes. The scribed electrodes were prepared without the use of any conductive additives and binders, and they were directly assembled in a coin cell. These `binder-less' scribed Si-CNT electrodes exhibited a very high discharge capacity in excess of 3000 mA h g-1 and a low first cycle irreversible loss (FIR) (19%). In addition, the electrodes also showed good cyclability with capacity retention of 76% at the end of 50 cycles corresponding to a fade rate of 0.48% loss per cycle rendering the technique attractive for suitable Li-ion applications.A novel electrode fabrication technique involving a manual scribing action of vertically aligned silicon coated multiwall carbon nanotubes (VASCNTs) on a copper foil have been developed as a viable approach to Li-ion battery electrodes. The scribed electrodes were prepared without the use of any conductive additives and binders, and they were directly assembled in a coin cell. These `binder-less' scribed Si-CNT electrodes exhibited a very high discharge capacity in excess of 3000 mA h g-1 and a low first cycle irreversible loss (FIR) (19%). In addition, the electrodes also showed good cyclability with capacity retention of 76% at the end of 50 cycles corresponding to a fade rate of 0.48% loss per cycle rendering the technique attractive for suitable Li-ion applications. Electronic supplementary information (ESI) available: (1) Video S1: video showing the preparation of the SiCNT pellets and subsequent scribing on copper foils to form the electrodes; (2) Fig. S2: TGA plot of CNT/Si heterostructures performed in air from 25 °C to 1000 °C at a heating rate of 10 °C min-1. See DOI: 10.1039/c4nr04288c

Background The aim of this work is to investigate the structure and function of enzymes immobilised on nanomaterials. This work will allow better understanding of enzyme-nanomaterial interactions, as well as designing functional protein-nanomaterial conjugates. Methodology/Principal Findings Multiwalled carbon nanotubes (MWNTs) were functionalised with amino groups to improve solubility and biocompatibility. The pristine and functionalised forms of MWNTs were characterised with Fourier-transform infrared spectroscopy. Thermogravimetric analysis was done to examine the degree of the functionalisation process. An immobilised biocatalyst was prepared on functionalised nanomaterial by covalent binding. Thermomyces lanuginosus lipase was used as a model enzyme. The structural change of the immobilised and free lipases were characterised with transmission electron Microscopy, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy and Circular dichroism spectroscopy. Biochemical characterisation of immobilised enzyme showed broader pH and thermal optima compared to soluble form. Reusability of the immobilised enzyme for hydrolysis of long chain esters was demonstrated up to ten cycles. Conclusion/Significance Lipase immobilised on MWNTs has exhibited significantly improved thermal stability. The exploration of advanced nanomaterial for enzyme immobilisation support using sophisticated techniques makes nanobiocatalyst of potential interest for biosensor applications. PMID:24069216

Electroactivity of polypyrrole hyaluronic acid, electropolymerized in the presence of oxidized carbon nanotubes (PPyHA-CNT) was studied in situ by electrochemical atomic force microscopy (EC-AFM) in physiological electrolyte solution. In situ Raman spectroscopic and quartz crystal microbalance (QCM) studies were conducted on layers of the polymer grown on AT-cut 5 MHz quartz crystals. Human adipose stem cell (ASC) attachment and viability were studied by Live/Dead staining, and the proliferation was evaluated by WST-1 Cell proliferation assay for polypyrrole samples electropolymerized on titanium. According to cyclic voltammetry, the measured specific capacitance of the material on gold is roughly 20% of the reference polypyrrole dodecylbenzene sulfonate (PPyDBS). Electrochemical-QCM (EC-QCM) analysis of a 210-nm thick film reveals that the material is very soft G' approximately 100 kPa and swells upon reduction. EC-AFM of samples polymerized on microelectrodes show that there are areas of varying electroactivity, especially for samples without a hydrophopic backing PPyDBS layer. AFM line scans show typically 20-25% thickness change during electrochemical reduction. Raman spectroscopic analysis suggests that the material supports noticeable polaron conduction. Biocompatibility study of the PPyHA-CNT on titanium with adipose stem cells showed equal or better cell attachment, viability, and proliferation compared with the reference polylactide. PMID:19753624

The dispersing power of surfactant-modified multiwalled carbon nanotubes (MWCNTs) and their effect on the antibacterial activity were examined. The MWCNTs were modified using a dioctyl sodium sulfosuccinate (AOT) surfactant. UV-vis spectroscopy and transmission electron microscopy (TEM) were used to characterize the dispersion of MWCNTs in the aqueous phase. Fourier transform infrared spectroscopy confirmed the results of UV-vis spectroscopy and TEM, indicating that the AOT molecules had been adsorbed successfully onto the MWCNT surface. The highly dispersed AOT-modified MWCNTs showed strong antibacterial activity to Streptococcus mutans. The fluorescence images showed that the AOT-modified MWCNTs were capable of capturing bacteria and forming cell aggregates as well as killing them. The optical density growth curves and colony-forming units assays confirmed that the antibacterial activity of the AOT-modified MWCNTs was concentration-dependent and treatment time-dependent. This finding might be useful for applications of AOT-modified MWCNTs as an antibacterial agent to eliminate pathogens from a biocontaminated water phase. PMID:21958539

We report synthesis of a highly versatile multicomponent nanosystem by covalently decorating the surface of multiwalled carbon nanotubes (CNTs) by magnetite nanoparticles (Fe3O4), poly(ethylene glycol) (PEG), and fluorophore fluorescein isothiocyanate (FITC). The resulting Fe3O4-PEG-FITC-CNT nanosystem demonstrates high dispersion ability in an aqueous medium, magnetic responsiveness, and fluorescent capacity. Transmission electron microscopy images revealed that Fe3O4 nanoparticles were well anchored onto the surfaces of the CNT. In vitro time kinetic experiments using confocal microscopy demonstrated a higher uptake of the Fe3O4-PEG-FITC-CNT nanosystem localized at the perinuclear region of MCF7 cells compared to the free FITC. In addition, the CNT nanosystem demonstrated no evidence of toxicity on cell growth. Surface conjugation of multicomponents, combined with in vitro non-toxicity, enhanced cellular uptake for FITC and site specific targeting ability makes this fluorescent Fe3O4-PEG-FITC-CNT nanosystem an ideal candidate for bioimaging, both in vitro and in vivo.

This thesis is concerned with the development of high performance ultrahigh molecular polyethylene (UHMWPE) fibers reinforced using multiwalled carbon nanotubes (MWCNTs). A novel process has been developed, whereby, MWCNT/UHMWPE nanocomposite fibers with Young's modulus up to 137 GPa and tensile strength of ˜4.2 GPa has been produced. This fiber possesses the best specific mechanical properties amongst all current commercial high performance fibers. Systematic investigations were carried out to elucidate the mechanisms of reinforcement. Firstly, systematical experimental studies were carried out to investigate the CNT reinforcing effect on nanocomposite fibers prepared with different PE molecular orientations. The overall effect can be classified into three regions. At low molecular orientation levels, the CNTs act to toughen and strengthen the nanocomposites. At the intermediate molecular orientations, the CNTs have negligible effects on the mechanical properties of the nanocomposites. At very high molecular orientations, the CNTs act to mainly stiffen and strengthen the nanocomposite. Secondly, systematic investigations were carried out to investigate the structure evolution as well as the load transfer between the embedded CNTs and that of the matrix PE. Thermal and morphological studies demonstrate that CNTs act as effective nucleation sites for PE crystal growth. The load transfer mechanisms in both the low and high molecular orientation fibers are similar. Major differences were related to CNT alignment effects. The highly oriented fibers show CNT alignment effect in the initial elastic regime, whereas the CNTs in the fibers of low molecular orientations show no appreciable alignment in the elastic regime. Finally, based on the experimental observations, a mechanistic model has been proposed to elucidate the reinforcement mechanisms. This model proposes that there exists an absorption layer surrounding CNTs. (Abstract shortened by UMI.)

Nitric oxide NO is one of the major targets for environmental monitoring, but the existing NO sensors are limited by their low sensitivity and narrow test range. Here, a NO gas sensor employing multiwalled carbon nanotubes (MWCNTs) was fabricated, and its properties in NO–N{sub 2} mixture were investigated from both emission and ionization. The current I{sub e} passing through the nanotubes cathode was found to decrease with increasing NO concentration and increase linearly in different slopes with the extracting voltage U{sub e}. It is shown that the Schottky barrier of the MWCNTs calculated by I{sub e} increased with NO concentration due to the adsorption of NO gas, which restrained the electron emission and consequently weakened the ionization. The positive ion currents I{sub c} passing through the collecting electrode at different voltages of U{sub e} were found to monotonically decrease with increasing NO concentration, which was induced by both of the reduced electron emission and the consumption of the two excited metastable states N{sub 2}(A{sup 3}∑{sub u}{sup +}) and N{sub 2}(a′{sup 1}∑{sub u}{sup −}) by NO. The sensor exhibited high sensitivity at the low temperature of 30 °C. The calculated conductivity was found to be able to take place of I{sub c} for NO detection in a wide voltage range of 80–150 V U{sub e}.

The aim of the present work is to determine the optical absorption cross section for visible radiation of various types of multiwall carbon nanotubes (MWCNTs) having different dimensions through macroscopic optical measurements. This is achieved by dispersing MWCNTs in polydimethylsiloxane (PDMS) and preparing composite films. Different percentages (0.0% to 1.5%) of each MWCNTs type were mixed into the PDMS matrix using high speed mechanical stirring (~1000 rpm) and ultrasonication (~37 kHz) to reach optimal dispersion. By using doctor blading technique, 100 µm thick uniform films were produced on glass. They were then thermally cured and detached from the glass to get flexible and self-standing films. Field-Emission Scanning Electron Microscope (FESEM) analysis of cryo-fractured composite samples was used to check the dispersion of MWCNTs in PDMS, while Raman spectroscopy and FTIR were employed to rule out possible structural changes of the polymer in the composite that would have altered its optical properties. Total and specular reflection and transmission spectra were measured for all films. The absorption coefficient, which represents the fractional absorption per unit length and is proportional to the concentration of absorbing sites (i.e., MWCNTs at photon energies upon which PDMS is non-absorbing), was extracted. For each MWCNTs type, the absorption cross section of an individual MWCNT was obtained from the slope of absorption coefficient versus MWCNTs number density curve. It was found to be related with MWCNT volume. This method can be applied to all other nanoparticles as far as they can be dispersed in a host transparent matrix. PMID:27398474

A simple, highly sensitive and selective carbon nanocomposite electrode has been developed for the electrochemical trace determination of cadmium. This sensor was designed by incorporation of multi-walledcarbon nanotubes (MWCNTs) and a new synthesized Schiff base into the carbon paste ionic liquid electrode (CPE(IL)) which provides remarkably improved sensitivity and selectivity for the electrochemical stripping assay of Cd(II). The detection limit of the method was found to be 0.08 μg L(-1) (S/N=3) that is lower than the maximum contaminant level of Cd(II) allowed by the Environmental Protection Agency (EPA) in standard drinking waters. The proposed electrode exhibits good applicability for monitoring Cd(II) in various real samples. PMID:24411345

As a result of the growing potential industrial and medical applications of multi-walledcarbon nanotubes (MWCNTs), people working in or residing near facilities that manufacture them may be exposed to airborne MWCNTs in the future. Because of concerns regarding their toxicity, quantitative data on the long-term clearance of pristine MWCNTs from the lungs are required. We administered pristine MWCNTs well dispersed in 0.5 mg ml(-1) Triton-X solution to rats at doses of 0.20 or 0.55 mg via intratracheal instillation and investigated clearance over a 12-month observation period. The pristine MWCNTs pulmonary burden was determined 1, 3, 7, 28, 91, 175 and 364 days after instillation using a method involving combustive oxidation and infrared analysis, combined with acid digestion and heat pretreatment. As 0.15- and 0.38-mg MWCNTs were detected 1 day after administration of 0.20 and 0.55 mg MWCNTs, respectively, approximately 30% of administrated MWCNTs may have been cleared by bronchial ciliary motion within 24 h of administration. After that, the pulmonary MWCNT burden did not decrease significantly over time for up to 364 days after instillation, suggesting that MWCNTs were not readily cleared from the lung. Transmission electron microscopy (TEM) showed that alveolar macrophages internalized the MWCNTs and retained in the lung for at least 364 days after instillation. MWCNTs were not detected in the liver or brain within the 364-day study period (<0.04 mg per liver, < 0.006 mg per brain). PMID:26712168

In view of several disadvantages as well as adverse effects associated with the use of chemical processes for producing esters, alternative techniques such as the utilization of enzymes on multi-walledcarbon nanotubes (MWCNTs), have been suggested. In this study, the oxidative MWCNTs prepared using a mixture of HNO3 and H2SO4 (1:3 v/v) were used as a supportive material for the immobilization of Candida rugosa lipase (CRL) through physical adsorption process. The resulting CRL-MWCNTs biocatalysts were utilized for synthesizing geranyl propionate, an important ester for flavoring agent as well as in fragrances. Enzymatic esterification of geraniol with propionic acid was carried out using heptane as a solvent and the efficiency of CRL-MWCNTs as a biocatalyst was compared with the free CRL, considering the incubation time, temperature, molar ratio of acid:alcohol, presence of desiccant as well as its reusability. It was found that the CRL-MWCNTs resulted in a 2-fold improvement in the percentage of conversion of geranyl propionate when compared with the free CRL, demonstrating the highest yield of geranyl propionate at 6h at 55°C, molar ratio acid: alcohol of 1:5 and with the presence of 1.0g desiccant. It was evident that the CRL-MWCNTs biocatalyst could be reused for up to 6 times before a 50% reduction in catalytic efficiency was observed. Hence, it appears that the facile physical adsorption of CRL onto F-MWCNTs has improved the activity and stability of CRL as well as served as an alternative method for the synthesis of geranyl propionate. PMID:25837507

Trans femoral amputation is one of the most uncomfortable surgeries in patient׳s life, where the prosthesis consisting of a socket, knee joint, pylon and foot is used to do the walking activities. The artificial prosthetic knee joint imitates the functions of human knee to achieve the flexion-extension for the above knee amputee. The objective of present work is to develop a light weight composite material for the knee joint to reduce the metabolic cost of an amputee. Hence, an attempt was made to study the mechanical properties of multiwalledcarbon nanotubes (MWCNT) reinforced Poly (methyl methacrylate) (PMMA) prepared through melt mixing technique and optimize the concentration of reinforcement. The PMMA nanocomposites were prepared by reinforcing 0, 0.1, 0.2, 0.25, 0.3 and 0.4 wt% of MWCNT using injection moulding machine via twin screw extruder. It is observed that the tensile and flexural strength of PMMA, which were studied as per ASTM D638 and D790, respectively, were increased by 32.9% and 26.3% till 0.25 wt% reinforcement of MWCNT. The experimental results of strength and modulus were compared with theoretical prediction, where a good correlation was noted. It is concluded that the mechanical properties of PMMA were found to be increased to maximum at 0.25 wt% reinforcement of MWCNT, where the Pukanszky model and modified Halpin-Tsai model are suggested to predict the strength and modulus, respectively, of the PMMA/MWCNT composite, which can be opted as a suitable materiel for the development of polycentric knee joint. PMID:26099200

Background Increasing concern has been expressed regarding the potential adverse health effects that may be associated with human exposure to inhaled multi-walledcarbon nanotubes (MWCNTs). Thus it is imperative that an understanding as to the underlying mechanisms and the identification of the key factors involved in adverse effects are gained. In the alveoli, MWCNTs first interact with the pulmonary surfactant. At this interface, proteins and lipids of the pulmonary surfactant bind to MWCNTs, affecting their surface characteristics. Aim of the present study was to investigate if the pre-coating of MWCNTs with pulmonary surfactant has an influence on potential adverse effects, upon both (i) human monocyte derived macrophages (MDM) monocultures, and (ii) a sophisticated in vitro model of the human epithelial airway barrier. Both in vitro systems were exposed to MWCNTs either pre-coated with a porcine pulmonary surfactant (Curosurf) or not. The effect of MWCNTs surface charge was also investigated in terms of amino (−NH2) and carboxyl (−COOH) surface modifications. Results Pre-coating of MWCNTs with Curosurf affects their oxidative potential by increasing the reactive oxygen species levels and decreasing intracellular glutathione depletion in MDM as well as decreases the release of Tumour necrosis factor alpha (TNF-α). In addition, an induction of apoptosis was observed after exposure to Curosurf pre-coated MWCNTs. In triple cell-co cultures the release of Interleukin-8 (IL-8) was increased after exposure to Curosurf pre-coated MWCNTs. Effects of the MWCNTs functionalizations were minor in both MDM and triple cell co-cultures. Conclusions The present study clearly indicates that the pre-coating of MWCNTs with pulmonary surfactant more than the functionalization of the tubes is a key factor in determining their ability to cause oxidative stress, cytokine/chemokine release and apoptosis. Thus the coating of nano-objects with pulmonary surfactant should be

Water-saturated column experiments were conducted to investigate the effect of input concentration (C₀) and sand grain size on the transport and retention of low concentrations (1, 0.01, and 0.005 mg L⁻¹) of functionalized ¹⁴C-labeled multi-walledcarbon nanotubes (MWCNT) under repulsive electrostatic conditions that were unfavorable for attachment. The breakthrough curves (BTCs) for MWCNT typically did not reach a plateau, but had an asymmetric shape that slowly increased during breakthrough. The retention profiles (RPs) were not exponential with distance, but rather exhibited a hyper-exponential shape with greater retention near the column inlet. The collected BTCs and RPs were simulated using a numerical model that accounted for both time- and depth-dependent blocking functions on the retention coefficient. For a given C₀, the depth-dependent retention coefficient and the maximum solid phase concentration of MWCNT were both found to increase with decreasing grain size. These trends reflect greater MWCNT retention rates and a greater number of retention locations in the finer textured sand. The fraction of the injected MWCNT mass that was recovered in the effluent increased and the RPs became less hyper-exponential in shape with higher C₀ due to enhanced blocking/filling of retention locations. This concentration dependency of MWCNT transport increased with smaller grain size because of the effect of pore structure and MWCNT shape on MWCNT retention. In particular, MWCNT have a high aspect ratio and we hypothesize that solid phase MWCNT may create a porous network with enhanced ability to retain particles in smaller grain sized sand, especially at higher C₀. Results demonstrate that model simulations of MWCNT transport and fate need to accurately account for observed behavior of both BTCs and RPs. PMID:23228890

A surface modification method was carried out to enhance the light crude oil sorption capacity of polyurethane foam (PUF) through immobilization of multi-walledcarbon nanotube (MWCNT) on the foam surface at various concentrations. The developed sorbent was characterized using scanning electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, and tensile elongation test. The results obtained from thermogravimetric and tensile elongation tests showed the improvement of thermal and mechanical resistance of surface-modified foam. The experimental data also revealed that the immobilization of MWCNT on PUF surface enhanced the sorption capacity of light crude oil and reduced water sorption. The highest oil removal capacity was obtained for 1 wt% MWCNT on PUF surface which was 21.44% enhancement in light crude oil sorption compared to the blank PUF. The reusability of surface modified PUF was determined through four cycles of chemical regeneration using petroleum ether. The adsorption of light crude oil with 30 g initial mass showed that 85.45% of the initial oil sorption capacity of this modified sorbent was remained after four regeneration cycles. Equilibrium isotherms for adsorption of oil were analyzed by the Freundlich, Langmuir, Temkin, and Redlich-Peterson models through linear and non-linear regression methods. Results of equilibrium revealed that Langmuir isotherm is the best fitting model and non-linear method is a more accurate way to predict the parameters involved in the isotherms. The overall findings suggested the promising potentials of the developed sorbent in order to be efficiently used in large-scale oil spill cleanup. PMID:25917559

The use of a thermochemical grafting approach provides a versatile means to functionalise as-synthesised, bulk multi-walledcarbon nanotubes (MWNTs) without altering their inherent structure. The associated retention of properties is desirable for a wide range of commercial applications, including for drug delivery and medical purposes; it is also pertinent to studies of intrinsic toxicology. A systematic series of water-compatible MWNTs, with diameter around 12 nm have been prepared, to provide structurally-equivalent samples predominantly stabilised by anionic, cationic, or non-ionic groups. The surface charge of MWNTs was controlled by varying the grafting reagents and subsequent post-functionalisation modifications. The degree of grafting was established by thermal analysis (TGA). High resolution transmission electron microscope (HRTEM) and Raman measurements confirmed that the structural framework of the MWNTs was unaffected by the thermochemical treatment, in contrast to a conventional acid-oxidised control which was severely damaged. The effectiveness of the surface modification was demonstrated by significantly improved solubility and stability in both water and cell culture medium, and further quantified by zeta-potential analysis. The grafted MWNTs exhibited relatively low bioreactivity on human immortal alveolar epithelial type 1-like cells (TT1) following 24h exposure as demonstrated by 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) and lactate dehydrogenase release (LDH) assays. The exposure of TT1 cells to MWNTs suppressed the release of the inflammatory mediators, interleukin 6 (IL-6) and interleukin 8 (IL-8). TEM cell uptake studies indicated efficient cellular entry of MWNTs into TT1 cells, via a range of mechanisms. Cationic MWNTs showed a more substantial interaction with TT1 cell membranes than anionic MWNTs, demonstrating a surface charge effect on cell uptake. PMID:24631251

To evaluate pulmonary toxicity of multi-walledcarbon nanotubes (MWCNTs), F344 rats of both sexes were exposed by inhalation to 0.2, 1 or 5 mg/m3 MWCNT aerosol for 6 h/day, 5 days/week for 2 weeks using a whole-body exposure system. At the end of the 2-week exposure period, one-half of the rats were necropsied, and at the end of an additional 4-week postexposure period, the remaining rats were necropsied. MWCNTs were deposited in the lungs of all MWCNT-exposed groups and mostly remained in the lungs throughout the 4-week postexposure period. Granulomatous changes in the lung were found in the rats exposed to 5 mg/m3 MWCNTs, and these changes were slightly aggravated at the end of the 4-week postexposure period. In the bronchoalveolar lavage fluid (BALF), the numbers of neutrophils, percentages of bi- and multinucleated alveolar macrophages, levels of ALP activity and concentrations of total protein and albumin were elevated in the rats exposed to 1 and 5 mg/m3 MWCNTs. At the end of the 4-week postexposure period, the values of the BALF parameters tended to remain elevated. In addition, goblet cell hyperplasias in the nasal cavity and nasopharynx were observed in the rats exposed to 1 and 5 mg/m3 MWCNTs, but these lesions had largely regressed by the end of the postexposure period. Based on the histopathological and inflammatory changes, the no-observed-adverse-effect level (NOAEL) for inhalation of MWCNTs for 2 weeks was 0.2 mg/m3. PMID:23914055

Aiming at the preparation of efficient, stable on storage and recyclable nanobiocatalysts for enantioselective transesterification, alkaline lipase from Pseudomonas fluorescens was covalently immobilized (up to 8.5wt.%) on functionalized multi-wallcarbon nanotubes (f-MWCNTs). f-MWCNTs were synthesized via: (a) (2+1)-cycloaddition of a nitrene to the C-sp(2) nanotube walls (3.2mmolg(-1), a novel synthetic approach) and, (b) oxidative treatments, i.e. Fenton reagent (3.5mmolg(-1)) and nitrating mixture (2.5mmolg(-1)), yielding aminoalkyl-, hydroxyl- and carboxyl-MWCNTs, respectively. Amino- and epoxy- functionalized mesoporous silica (f-SBA-15) were used as the reference supports. Transesterification of vinyl n-butyrate by racemic Solketal with a chromatographically (GC) traced kinetics was selected as the model reaction. The studies revealed that different chemical functionalization of morphologically identical nanotube supports led to various enzyme loadings, catalytic activities and enantioselectivities. MWCNT-NH2-based nanobiocatalyst was found to be the most active composite among all of the tested systems (yield 20%, t=0.5h, 1321Ug(-1)), i.e. 12 times more active than the native enzyme. In turn, lipase immobilized on MWCNT-COOH emerged as the most enantioselective system (ex aequo with SBA-NH2) (eeR=74%, t=0.5h at yield of 3-5%). The activity of the MWCNT-NH2-based nanobiocatalyst after 8 cycles of transesterification dropped to 60% of its initial value, whereas for SBA-NH2-based composite remained unchanged. Importantly, stability on storage was fully maintained for all MWCNT-based nanobiocatalysts or even 'extra-enhanced' for MWCNT-OH. PMID:27178796

The polyamide-based thermoplastic elastomers (Pebax®) were melt compounded with multi-walledcarbon nanotubes (MWNTs: 0.25˜5 wt%) and the variation of rheological and physical properties with MWNT contents was investigated. The crystallization temperature (Tc) of the nanocomposites with 0.5 wt% MWNTs was most increased by ca. 8oC, but it was decreased by further addition. In addition, the presence of MWNTs broadened the Tc peak with increasing nanotube contents. In contrast, the melting behavior was little influenced by the presence of MWNTs for all compositions. The incorporation of MWNTs increased the complex viscosity with MWNT contents and the abrupt increase was observed from 1 wt%. In addition, lower Newtonian flow region became disappearing with increasing MWNT contents, exhibiting notable shear thinning behavior from 1 wt% loading. Storage modulus was increased with MWNT contents in a similar manner to viscosity. Casson plot demonstrated a non-zero positive intercept for all the samples. In particular, the abrupt increase of yield stress was observed from 1 wt% loading. In the Cole-Cole plot, the nanocomposites gave a deviated curve from pure Pebax and the slope was decreased with increasing MWNT contents. The relaxation time calculated from viscoelastic parameters was increased with nanotube contents, but the increasing extents were reduced with increasing frequency. From 2 wt% MWNTs, the electrical conductivity was observed, indicating that the electrical percolation existed between 1.5 and 2 wt%. At 0.25 wt% loading the tensile strength was slightly increased, but it was gradually decreased by further addition. The introduction of MWNTs increased the tensile modulus with nanotube contents. In addition, ductile properties were reduced with increasing MWNT contents, resulting in low toughness.

Given the increasing use of carbon nanotubes (CNT) in composite materials and their possible expansion to new areas such as nanomedicine which will both lead to higher human exposure, a better understanding of their potential to cause adverse effects on human health is needed. Like other nanomaterials, the biological reactivity and toxicity of CNT were shown to depend on various physicochemical characteristics, and length has been suggested to play a critical role. We therefore designed a comprehensive study that aimed at comparing the effects on murine macrophages of two samples of multi-walled CNT (MWCNT) specifically synthesized following a similar production process (aerosol-assisted CVD), and used a soft ultrasonic treatment in water to modify the length of one of them. We showed that modification of the length of MWCNT leads, unavoidably, to accompanying structural (i.e. defects) and chemical (i.e. oxidation) modifications that affect both surface and residual catalyst iron nanoparticle content of CNT. The biological response of murine macrophages to the two different MWCNT samples was evaluated in terms of cell viability, pro-inflammatory cytokines secretion and oxidative stress. We showed that structural defects and oxidation both induced by the length reduction process are at least as responsible as the length reduction itself for the enhanced pro-inflammatory and pro-oxidative response observed with short (oxidized) compared to long (pristine) MWCNT. In conclusion, our results stress that surface properties should be considered, alongside the length, as essential parameters in CNT-induced inflammation, especially when dealing with a safe design of CNT, for application in nanomedicine for example. PMID:23181604

The fibrous shape and biopersistence of multi-walledcarbon nanotubes (MWCNT) have raised concern over their potential toxicity after pulmonary exposure. As in vivo exposure to MWCNT produced a transient inflammatory and progressive fibrotic response, this study sought to identify significant biological processes associated with lung inflammation and fibrosis pathology data, based upon whole genome mRNA expression, bronchoaveolar lavage scores, and morphometric analysis from C57BL/6J mice exposed by pharyngeal aspiration to 0, 10, 20, 40, or 80 μg MWCNT at 1, 7, 28, or 56 days post-exposure. Using a novel computational model employing non-negative matrix factorization and Monte Carlo Markov Chain simulation, significant biological processes with expression similar to MWCNT-induced lung inflammation and fibrosis pathology data in mice were identified. A subset of genes in these processes was determined to be functionally related to either fibrosis or inflammation by Ingenuity Pathway Analysis and was used to determine potential significant signaling cascades. Two genes determined to be functionally related to inflammation and fibrosis, vascular endothelial growth factor A (vegfa) and C-C motif chemokine 2 (ccl2), were confirmed by in vitro studies of mRNA and protein expression in small airway epithelial cells exposed to MWCNT as concordant with in vivo expression. This study identified that the novel computational model was sufficient to determine biological processes strongly associated with the pathology of lung inflammation and fibrosis and could identify potential toxicity signaling pathways and mechanisms of MWCNT exposure which could be used for future animal studies to support human risk assessment and intervention efforts. - Highlights: • A novel computational model identified toxicity pathways matching in vivo pathology. • Systematic identification of MWCNT-induced biological processes in mouse lungs • MWCNT-induced functional networks of lung

Multi-wallcarbon nanotubes (MWCNT) are a form of flexible fibrous nanomaterial with high electrical and thermal conductivity. However, 50-nm MWCNT in diameter causes malignant mesothelioma (MM) in rodents and, thus, the International Agency of Research on Cancer has designated them as a possible human carcinogen. Little is known about the molecular mechanism through which MWCNT causes MM. To elucidate the carcinogenic mechanisms of MWCNT in mesothelial cells, we used a variety of lysates to comprehensively identify proteins specifically adsorbed on pristine MWCNT of different diameters (50 nm, NT50; 100 nm, NT100; 150 nm, NT150; and 15 nm/tangled, NTtngl) using mass spectrometry. We identified >400 proteins, which included hemoglobin, histone, transferrin and various proteins associated with oxidative stress, among which we selected hemoglobin and transferrin for coating MWCNT to further evaluate cytotoxicity, wound healing, intracellular catalytic ferrous iron and oxidative stress in rat peritoneal mesothelial cells (RPMC). Cytotoxicity to RPMC was observed with pristine NT50 but not with NTtngl. Coating NT50 with hemoglobin or transferrin significantly aggravated cytotoxicity to RPMC, with an increase in cellular catalytic ferrous iron and DNA damage also observed. Knockdown of transferrin receptor with ferristatin II decreased not only NT50 uptake but also cellular catalytic ferrous iron. Our results suggest that adsorption of hemoglobin and transferrin on the surface of NT50 play a role in causing mesothelial iron overload, contributing to oxidative damage and possibly subsequent carcinogenesis in mesothelial cells. Uptake of NT50 at least partially depends on transferrin receptor 1. Modifications of NT50 surface may decrease this human risk. PMID:26679080

The adsorption of Cu(II) on oxidized multi-walledcarbon nanotubes (oMWCNTs) as a function of contact time, pH, ionic strength, temperature, and hydroxylated fullerene (C60(OH)n) and carboxylated fullerene (C60(C(COOH)2)n) were studied under ambient conditions using batch techniques. The results showed that the adsorption of Cu(II) had rapidly reached equilibrium and the kinetic process was well described by a pseudo-second-order rate model. Cu(II) adsorption on oMWCNTs was dependent on pH but independent of ionic strength. Compared with the Freundlich model, the Langmuir model was more suitable for analyzing the adsorption isotherms. The thermodynamic parameters calculated from temperature-dependent adsorption isotherms suggested that Cu(II) adsorption on oMWCNTs was spontaneous and endothermic. The effect of C60(OH)n on Cu(II) adsorption of oMWCNTs was not significant at low C60(OH)n concentration, whereas a negative effect was observed at higher concentration. The adsorption of Cu(II) on oMWCNTs was enhanced with increasing pH values at pH < 5, but decreased at pH ≥ 5. The presence of C60(C(COOH)2)n inhibited the adsorption of Cu(II) onto oMWCNTs at pH 4–6. The double sorption site model was applied to simulate the adsorption isotherms of Cu(II) in the presence of C60(OH)n and fitted the experimental data well. PMID:24009683

Polydimethylsiloxane (PDMS) with exceptional fouling-release properties is extremely susceptible to the microfouling resulted from the colonization of the pioneer microorganisms in the marine environment. In this study, six carboxyl-modified multi-walledcarbon nanotubes (cMWNTs) nanoparticles were incorporated into the PDMS matrix, respectively, in order to produce the cMWNTs-filled PDMS nanocomposites (CPs) with improved antifouling (AF) properties. The AF properties of the six CPs were examined via the field assays conducted in Weihai, China. The effects of the anti-biofouling potential of the CPs (i.e. the P3 surface) on the colonization of the pioneer prokaryotic and eukaryotic microbes were investigated using the single-stranded conformation polymorphism technique via the comparison of the diversity indices. Different CPs have displayed differential and better AF properties as compared to that of the unfilled PDMS (P0). The P3 surface has exhibited exceptional anti-biofouling capacity compared with the other CPs surfaces, which can effectively prevent biofouling for more than 14 weeks in the field. The SSCP analysis revealed that the P3 surface may have significant modulating effect on the pioneer microbial communities. The pioneer eukaryotic microbes seemed more susceptible than the pioneer prokaryotic microbes to be subjected to the major perturbations exerted by the P3 surface. The dramatically reduced eukaryotic-microbial diversity may contribute to the impeding and weakening of the development and growth of the biofilm. The P3 surface has the potential to be used for future maritime applications. PMID:27430515

An effectively and functionally magnetic multi-walledcarbon nanotube (MWCNTs) nano-composite (APCNT-KOH) was synthesized by a one-pot and facile method. The residual Fe catalyst particles of the as-prepared MWCNTs were utilized as magnetic materials through KOH activation. The resulting APCNT-KOH exhibited very high adsorption capacities for toluene (T), ethylbenzene (E), and xylene (X) (TEX) pollutants than many other adsorbents, because of their large specific surface area and high degree of surface activity. The adsorption process was found to be pH, ionic strength, and temperature dependent, and the maximum adsorption capacity was observed at pH 6 for TEX pollutants. The adsorption isotherm data were analyzed by applying the Langmuir, Freundlich, and Dubinin-Radushkevich isothermal models. The Langmuir model showed the best fit to the experimental isotherm data with a maximum adsorption capacity(qm,toluene = 63.34 mg/g, qm, ethylbenzene = 249.44 mg/g, qm,m-xylene = 227.05 mg/g, qm,o-xylene = 138.04 mg/g, qm,p-xylene = 105.59 mg/g). Adsorption kinetics of TEX on APCNT-KOH was appropriately described by the pseudo-second-order rate model. The desorption experiments revealed the typical adsorption-desorption hysteresis, indicating that the adsorption and desorption processes of TEX undergo different pathways due to porous structure changes before and after adsorption and desorption. Collective results demonstrate that the functionalized magnetic APCNT-KOH composites are highly-effective adsorbents for TEX removal, which provides a promising and green route for MWCNTs in wastewater treatment. PMID:26714299

Multi-walledcarbon nanotubes (MWCNTs) have received considerable attention as reinforcement for composites due to their high tensile strength, stiffness, electrical conductivity and thermal conductivity as well as their low coefficient of thermal expansion. However, despite the availability of huge quantities of low-cost, commercially synthesized nanotubes, the utilization of MWCNTs in engineering composites is extremely limited due to difficulties in achieving uniform dispersion and strong interfacial bonding with the matrix. A proven method of enhancing the nanotube-polymer interface and degree of MWCNT dispersion involves functionalizing the MWCNTs through oxidation with strong acids. While effective at laboratory scales, this technique is not well-suited for large-scale operations due to long processing times, poor yield, safety hazards, and environmental concerns. This work aims to find scalable solutions to several of the challenges associated with the fabrication of MWCNT-reinforced composites. For polymer matrix composite applications, a rapid, dry, and cost-effective method of oxidizing MWCNTs with O3 in a fluidized bed was developed as an alternative to acid oxidation. Oxidized MWCNTs were further functionalized with silane coupling agents using water and supercritical carbon dioxide as solvents in order to endow the MWCNTs with matrix-specific functionalities. The effect of silanization on the cure kinetics, rheological behavior, and thermo-mechanical properties of model epoxy nanocomposites were investigated. Small additions of functionalized MWCNTs were found to increase the glass transition temperature, strength, and toughness of the epoxy. In order to achieve composite properties approaching those of individual nanotubes, new approaches are needed to allow for high loadings of MWCNTs. One strategy involves making macroscopic mats of nanotubes called buckypaper (BP) and subsequently infiltrating the mats with resin in processes familiar to

Background The exceptional physical-chemical properties of carbon nanotubes have lead to their use in diverse commercial and biomedical applications. However, their utilization has raised concerns about human exposure that may predispose individuals to adverse health risks. The present study investigated the susceptibility to cardiac ischemic injury following a single exposure to various forms of multi-walledcarbon nanotubes (MWCNTs). It was hypothesized that oropharyngeal aspiration of MWCNTs exacerbates myocardial ischemia and reperfusion injury (I/R injury). Methods Oropharyngeal aspiration was performed on male C57BL/6J mice with a single amount of MWCNT (0.01 - 100 μg) suspended in 100 μL of a surfactant saline (SS) solution. Three forms of MWCNTs were used in this study: unmodified, commercial grade (C-grade), and functionalized forms that were modified either by acid treatment (carboxylated, COOH) or nitrogenation (N-doped) and a SS vehicle. The pulmonary inflammation, serum cytokine profile and cardiac ischemic/reperfusion (I/R) injury were assessed at 1, 7 and 28 days post-aspiration. Results Pulmonary response to MWCNT oropharyngeal aspiration assessed by bronchoalveolar lavage fluid (BALF) revealed modest increases in protein and inflammatory cell recruitment. Lung histology showed modest tissue inflammation as compared to the SS group. Serum levels of eotaxin were significantly elevated in the carboxylated MWCNT aspirated mice 1 day post exposure. Oropharyngeal aspiration of all three forms of MWCNTs resulted in a time and/or dose-dependent exacerbation of myocardial infarction. The severity of myocardial injury varied with the form of MWCNTs used. The N-doped MWCNT produced the greatest expansion of the infarct at any time point and required a log concentration lower to establish a no effect level. The expansion of the I/R injury remained significantly elevated at 28 days following aspiration of the COOH and N-doped forms, but not the C-grade as

LSER models for organic compounds adsorption by single and multi-walledcarbon nanotubes and activated carbon were successfully developed. The cavity formation and dispersion interactions (vV), hydrogen bond acidity interactions (bB) and π-/n-electron interactions (eE) are the most influential adsorption mechanisms. SWCNTs is more polarizable, less polar, more hydrophobic, and has weaker hydrogen bond accepting and donating abilities than MWCNTs and AC. Compared with SWCNTs and MWCNTs, AC has much less hydrophobic and less hydrophilic adsorption sites. The regression coefficients (e, s, a, b, v) vary in different ways with increasing chemical saturation. Nonspecific interactions (represented by eE and vV) have great positive contribution to organic compounds adsorption, and follow the order of SWCNTs > MWCNTs > AC, while hydrogen bond interactions (represented by aA and bB) demonstrate negative contribution. These models will be valuable for understanding adsorption mechanisms, comparing adsorbent characteristics, and selecting the proper adsorbents for certain organic compounds. PMID:26319510

This work expands the redox chemistry of single-wall carbon nanotubes (SWCNTs) by investigating its role in a number of SWCNT sorting processes. Using a polyethylene glycol (PEG)/dextran (DX) aqueous two-phase system, we show that electron-transfer between redox molecules and SWCNTs triggers reorganization of the surfactant coating layer, leading to strong modulation of nanotube partition in the two phases. While the DX phase is thermodynamically more favored by an oxidized SWCNT mixture, the mildly reducing PEG phase is able to recover SWCNTs from oxidation and extract them successively from the DX phase. Remarkably, the extraction order follows SWCNT bandgap: semiconducting nanotubes of larger bandgap first, followed by semiconducting nanotubes of smaller bandgap, then nonarmchair metallic tubes of small but nonvanishing bandgap, and finally armchair metallic nanotubes of zero bandgap. Furthermore, we show that redox-induced surfactant reorganization is a common phenomenon, affecting nanotube buoyancy in a density gradient field, affinity to polymer matrices, and solubility in organic solvents. These findings establish redox modulation of surfactant coating structures as a general mechanism for tuning a diverse range of SWCNT sorting processes and demonstrate for the first time that armchair and nonarmchair metallic SWCNTs can be separated by their differential response to redox. PMID:25719939

Piezoelectric sensors and actuators are needed for a wide range of applications from physiological measurement to industrial monitoring systems. Sensors that can be easily integrated with the host, while maintaining high sensitivity and reliability over a wide range of frequencies are not readily feasible and economical with homogenous piezoelectric materials. It is well known that two-phase piezoelectric-epoxy composites offer several benefits over their single phase counterparts, as the properties of the constituent phases combine to improve the range of applicability. However, the piezoelectric properties of these materials suffer from the electrically insulating properties of the epoxy matrix. The electrical properties of the matrix may be enhanced by including electrically conducting inclusions however, less is known about the mechanisms that drive the changes in these properties. Hence, this experimental investigation of sensor materials builds on the previous work in two-phase piezoelectric composites, where the aims are to understand the roles that specific fabrication parameters and inclusion composition play in determining the piezoelectric and dielectric performance the aforementioned composites. The materials under investigation will be comprised of Lead Zirconate Titanate, Epofix Cold-Setting Embedding Resin and multi-walledcarbon nanotubes, i.e. the piezoelectric, epoxy and electrical inclusions respectively. Our work suggests that inclusion of MWCNTs enhances the piezoelectric and dielectric properties with increasing volume fraction below the percolation threshold. This work seeks to understand how the processing parameters: poling temperature, poling type and particle distribution influence the contact resistance, space charge double layer at the piezoelectric and conductor interfaces and electric field intensity at the piezoelectric boundary, which all ultimately dictate the piezoelectric and dielectric performance of the composite materials

Composites of multi-walledcarbon nanotubes (MWCNTs) with polypropylene (PP) and thermoplastic olefins (TPOs) were prepared by melt compounding. Two non-covalent functionalization methods were employed to improve nanotube dispersion and the resulting composite properties are reported. The first functionalization approach involved partial coating of the surface of the nanotubes with a hyperbranched polyethylene (HBPE). MWCNT functionalization with HBPE was only moderately successful in breaking up the large aggregates that formed upon melt mixing with PP. In spite of the formation of large aggregates, the samples were conductive above a percolation threshold of 7.3 wt%. MWCNT functionalization did not disrupt the electrical conductivity of the nanotubes. The composite strength was improved with addition of nanotubes, but ductility was severely compromised because of the existence of aggregates. The second method involved PP matrix functionalization with aromatic moieties capable of pi-pi interaction with MWCNT sidewalls. Various microscopy techniques revealed the addition of only 25 wt% of PP-g-pyridine (Py) to the neat PP was capable of drastically reducing nanotube aggregate size and amount. Raman spectroscopy confirmed improved polymer/nanotube interaction with the PP-g-Py matrix. Electrical percolation threshold was obtained at a MWCNT loading of approximately 1.2 wt%. Electrical conductivity on the order of 10 -2 S/m was achieved, suggesting possible use in semi-conducting applications. Composite strength was improved upon addition of MWCNTs. The matrix functionalization with Py resulted in a significant improvement in composite ductility when filled with MWCNTs in comparison to its maleic anhydride (MA) counterpart. Preliminary investigations suggest that the use of alternating current (AC) electric fields may be effective in aligning nanotubes in PP to reduce the filler loading required for electrical percolation. Composites containing MWCNT within PP

Carbon nanotubes (CNTs) are currently used in numerous industrial and biomedical applications. Recent studies suggest that workers may be at risk of adverse health effects if they are exposed to CNTs. A National Institute for Occupational Safety and Health (NIOSH) survey of the carbonaceous nanomaterial industry found that 77% of the companies used respiratory protection. Elastomeric half-mask respirators and filtering facepiece respirators (FFRs) are commonly used. Although numerous respirator filtration studies have been done with surrogate engineered nanoparticles, such as sodium chloride, penetration data from engineered nanoparticles such as CNTs are lacking. The aims of this study were to develop a new CNT aerosol respirator testing system and to determine multi-walled CNT (MWCNT) penetration through FFRs. A custom-designed CNT aerosol respirator testing system (CNT-ARTS) was developed which was capable of producing a sufficient amount of airborne MWCNTs for testing of high efficiency FFRs. The size distribution of airborne MWCNTs was 20–10,000 nm, with 99% of the particles between 25 and 2840 nm. The count median diameter (CMD) was 209 nm with a geometric standard deviation (GSD) of 1.98. This particle size range is similar to those found in some work environments (particles ≤6000 nm). The penetration of MWCNTs through six tested FFR models at two constant flow rates of 30 and 85 LPM was determined. Penetration at 85 LPM (0.58–2.04% for N95, 0.15–0.32% for N99, and 0.007–0.009% for P100 FFRs) was greater compared with the values at 30 LPM (0.28–1.79% for N95, 0.10–0.24% for N99, and 0.005–0.006% for P100 FFRs). The most penetrating particle size through all six tested FFR models was found to be in the range of 25–130 nm and 35–200 nm for the 30-LPM and 85-LPM flow rates, respectively. PMID:26166842

Biodegradable nanocomposite based on poly(butylene succinate) (PBSU) and multi-walledcarbon nanotubes (MWNTs) was prepared by solution blending method at 1 wt% MWNTs loading. Scanning electron microscopic observation illustrates a homogeneous distribution of MWNTs in the PBSU matrix. Differential scanning calorimetry, optical microscopy, and wide angle X-ray diffraction were used to study the nonisothermal crystallization, isothermal crystallization kinetics, spherulitic morphology, and crystal structure of neat PBSU and its nanocomposite. The presence of MWNTs enhances the crystallization of PBSU in the nanocomposite due to the heterogeneous nucleation effect while the crystallization mechanism and crystal structure of PBSU do not change. Moreover, the incorporation of a small quantity of MWNTs has improved significantly the mechanical property of PBSU in the nanocomposite compared with that of neat PBSU. PMID:20352743

On the basis of spectra obtained through the X-ray Auger-electron spectroscopy (XAES) of carbon (C KVV) and X-ray photoelectron spectroscopy (XPS) of the carbon valence band using the equipment of the Russian-German beam line of the synchrotron radiation facility BESSY II and a Kratos Axis Ultra DLD analytical system, the influence of pulsed ion radiation on the ratio of sp2/sp3-hybridized orbitals of carbon atoms in layers of oriented multi-walledcarbon nanotubes (MWCNTs) is investigated. It is shown that when the MWCNTs are subjected to ten pulses, a substantial increase in the proportion of carbon atoms in the sp3 hybridization state occurs compared with MWCNTs subjected to a single pulse. This increase is associated with the formation of thin (<10 nm) nanotubes and onion-like carbon, inside which masses of nanodiamond structures are observed in some cases.

A new chemically modified carbon paste electrode (CMCPE) was applied to the simple, rapid, highly selective and sensitive determination of citalopram in human serum and pharmaceutical preparations using adsorptive square wave voltammetry (ASWV). The ZnO nanoparticles and multi-walledcarbon nanotubes modified CPE (ZnO-MWCNT/CPE) electrode was prepared by incorporation of the ZnO nanoparticles and multi-walledcarbon nanotubes (MWCNT) in carbon paste electrode. The limit of detection and the linear range were found to be 0.005 and 0.012 to 1.54μmolL(-1) of citalopram, respectively. The effects of potentially interfering substances on the determination of this compound were investigated and found that the electrode is highly selective. The proposed CMCPE was used to the determination of citalopram in human serum, urine and pharmaceutical samples. This reveals that ZnO-MWCNT/CPE shows excellent analytical performance for the determination of citalopram in terms of very low detection limit, high sensitivity, very good repeatability and reproducibility over other methods reported in the literature. PMID:26652440

The novel 3D graphene oxide/multi-walledcarbon nanotubes/ZnO nanocrystalline aggregate (GR/MWNTs/ZnO) hybrids were prepared by a spray drying method, and their adsorption and photocatalytic degradation for methyl orange (MO) were studied. Experimental results show that the synthetic GR/MWNTs/ZnO nanohybrids exhibited very strong adsorption capacity and high photocatalytic activity for MO. The maximum adsorption capacity of GR/MWNTs/ZnO sample reached 106.2 mg/g, and the photocatalytic efficiency of ZnO nanocrystallines was improved about one time by GR/MWNTs hybrids.

Long carbon nanotubes (CNTs) resemble asbestos fibers due to their high length to diameter ratio and they thus have genotoxic effects. Another parameter that might explain their genotoxic effects is contamination with heavy metal ions. On the other hand, short (1–2 μm) CNTs do not resemble asbestos fibers, and, once purified from contaminations, they might be suitable for medical applications. To identify the role of fiber thickness and surface properties on genotoxicity, well-characterized short pristine and carboxylated single-walled (SCNTs) and multi-walled (MCNTs) CNTs of different diameters were studied for cytotoxicity, the cell’s response to oxidative stress (immunoreactivity against hemoxygenase 1 and glutathione levels), and in a hypoxanthine guanine phosphoribosyltransferase (HPRT) assay using V79 chinese hamster fibroblasts and human lung adenocarcinoma A549 cells. DNA repair was demonstrated by measuring immunoreactivity against activated histone H2AX protein. The number of micronuclei as well as the number of multinucleated cells was determined. CNTs acted more cytotoxic in V79 than in A549 cells. Plain and carboxylated thin (<8 nm) SCNTs and MCNTs showed greater cytotoxic potential and carboxylated CNTs showed indication for generating oxidative stress. Multi-walled CNTs did not cause HPRT mutation, micronucleus formation, DNA damage, interference with cell division, and oxidative stress. Carboxylated, but not plain, SCNTs showed indication for in vitro DNA damage according to increase of H2AX-immunoreactive cells and HPRT mutation. Although short CNTs presented a low in vitro genotoxicity, functionalization of short SCNTs can render these particles genotoxic. PMID:25505129

The motivation of this thesis is to investigate the role of multi-walledcarbon nanotube (MWCNT) in enhancing the interlaminar shear strength (ILSS) of hybrid composites. The objective of this thesis is to understand the relationships between processing history, material variability, matrix properties, glass fiber/matrix interface properties and their correlations with interlaminar shear strength of hybrid composites. The interlaminar shear strength (ILSS) of hybrid composites made from glass fiber and multi-walledcarbon nanotube (MWCNT) modified epoxy is compared with that for unmodified epoxy/glass fiber composites (control). By combining the techniques of high speed mechanical stirring and ultrasonic agitation, 0.5% MWCNT by weight were dispersed in epoxy to prepare a suspension. Composites were manufactured by both injection double vacuum-assisted resin transfer molding (IDVARTM) and the flow flooding chamber (FFC) methods. Compression shear tests (CST) were conducted on the manufactured samples to determine the ILSS. The effect of processing history and batch-to-batch variability of materials---glass fiber preform, resin and carbon nanotubes---on the ILSS of samples made by both techniques was investigated. Statistical comparison of the measured ILSS values for hybrid composites with the control specimens clearly show that hybrid composites made by the FFC process resulted in significant ILSS enhancement relative to the control and the IDVARTM specimens. After it was established that the FFC process improved the ILSS, the effect of functionalizing the nanotubes was explored. Multiwalledcarbon nanotubes (MWCNT) were oxidized by acid treatment and heated with triethylene tetra amine (TETA) to obtain amino functionalized MWCNTs (f-MWCNT). Hybrid composites with f-MWCNTs were manufactured using FFC technique and control samples were fabricated using the same E-Glass fiber mat and unmodified epoxy resin subjected to the same processing history. CST results show

MOF-5 was synthesized by solvothermal method and its reactivation under anhydrous conditions. This research is conducted to investigate the effect of MOF-5 and MOF-5 modified with multi-wallcarbon nanotubes (MWCNTs) and expandable graphite (EG) on the performance of CO{sub 2} adsorption. The synthesized MOFs were characterized using Field emission scanning electron microscopy (FESEM) for surface morphology, Thermogravimetric analysis (TGA) for thermal stability, X-ray diffraction (XRD) for crystals plane, Brunauer-Emmet-Teller (BET) for surface area and CO{sub 2} adsorption. The result had showed that the modified MOF-5 enhanced the CO{sub 2} adsorption compared to the pure MOF-5. The increment in the CO{sub 2} uptake capacities of MOF materials was attributed to the decrease in the pore size and enhancement of micropore volume of MOF-5 by multi-walledcarbon nanotube and EG incorporation. The BET surface area of the synthesized MOF-5@MWCNTs is more than MOF-5. The CO{sub 2} sorption capacities of MOF-5 and MOF-5@MWCNTs were observed to increase from 0.00008 to 0.00048 mol g-1 at 298 K and 1 bar. The modified MOF-5@MWCNTs resulted in the highest CO{sub 2} adsorption followed by the modified MOF-5@ EG and lastly, MOF-5.

In the present work, a rapid and simple procedure was developed and validated for the analysis of trans-resveratrol in vegetable oils based on magnetic hydrophilic multi-walledcarbon nanotubes (h-MWCNT-MNPs) combined with liquid chromatography-tandem mass spectrometry (LC-MS/MS). h-MWCNT-MNPs were simply obtained by wrapping amine-functionalized Fe3O4 magnetic nanoparticles into previously oxidized hydrophilic multi-walledcarbon nanotubes. The major parameters affecting extraction efficiency were investigated, including the type and volume of desorption solvents, extraction and desorption time, washing solution, and sorbent amount. The limit of detection (LOD) and the limit of quantification (LOQ) were calculated as 0.6 and 2.0 μg/kg, respectively. The recoveries of trans-resveratrol in oil samples were in the range of 90.0-110.0% with RSDs of less than 17.5%. The results showed that only peanut oil contained trans-resveratrol, ranging from 8 ± 1 to 103 ± 12 μg/kg. The proposed method is reliable and robust, having an excellent potential for the analysis of trans-resveratrol in edible oils. PMID:25704710

Pt/Ru deposited on multi-walledcarbon nano-tubes (MWCNTs) was prepared with water/iso-propanol solutions containing Pt(IV) and Ru(III) ions by γ-irradiation. The water/iso-propanol ratio (v/v), additive amount of surfactant, the concentration ratio of Pt(IV)/Ru(III) ions and the total absorbed doses (kGy) were evaluated as synthesis parameters. The sample morphology was characterized by SEM and the Pt/Ru atomic ratio was obtained by EDX. It has been found that multi-walledcarbon nano-tubes can be well distributed in the water/iso-propanol solution with additive of surfactant. Pt(IV) and Ru(III) ions can be reduced by both of hydrated electron and radical of iso-propanol produced from hydrogen abstraction reaction. The Pt/Ru atom ratio can be controlled by changing the ratio of Pt(IV)/Ru(III). Small nano-particles of Pt/Ru deposited on MWCNTs can be obtained for possible application of electro-catalysts in the proton exchange membrane fuel cells (PEMFC) under optimum conditions with absorbed doses, amount of surfactant, water/iso-propanol ratio and so on. The reduction of Pt(IV)/Ru(III) ions in the aqueous solution with additive of surfactant was also studied by use of pulse radiolysis and the mechanism involved in the reduction process has been proposed.

The chemical modification of multi-wallcarbon nanotubes (MWNTs) is an emerging area in material science. In the present study, hydroxyl functionalized nickel(II) Schiff-base has been covalently anchored on modified MWNTs. The new modified MWNTs have been characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron (XPS), thermal analysis, UV-vis, diffuse reflectance (DRS), FT-IR spectroscopy and elemental analysis. The results suggest that the symmetrical Schiff-base; N, N'-bis(4-hydroxysalicylidene)-ethylene-1,2-diamine; H 2[(OH) 2-salen]; is a bivalent anion with tetradentate N 2O 2 donors derived from the phenolic oxygen and azomethine nitrogen. The formula was found to be [Ni((OH) 2-salen)] for the 1:1 non-electrolytic complex. Multi-wallcarbon nanotubes covalently anchored nickel(II) complex ([Ni((OH) 2-salen)]@MWNTs) catalyze the oxidation of phenol with H 2O 2. Oxidation of phenol catalyzed by this complex gave catechol and hydroquinone as major products. A suitable reaction condition has been optimized for [Ni((OH) 2-salen)]@MWNTs by considering the effect of various parameters such as reaction time and amount of oxidant, different solvents, concentration of substrate, etc. for the maximum transformation of phenol.

A novel magnetic carboxylated multi-walledcarbon nanotubes (c-MWCNT-MNPs) was proposed for magnetic solid-phase extraction coupled with liquid chromatography-tandem mass spectrometry to determine phenolic compounds in sesame oil. In this study, c-MWCNT-MNPs were acquired by simply dispersing Fe3O4 magnetic nanoparticles into carboxylated multi-walledcarbon nanotubes. The major parameters affecting extraction efficiency were optimized, including the type and volume of desorption solvents, extraction and desorption time, washing solution, and sorbent amount. The limit of quantifications and limit of detections were from 0.03μg/kg to 43.00μg/kg and from 0.01μg/kg to 13.60μg/kg, respectively. The recoveries of phenolic compounds in vegetable oils were in the range of 83.8-125.9% with inter-day and intra-day precisions of less than 13.2%. It was confirmed that this method was simple, rapid and reliable with an excellent potential for routine analysis of phenolic compounds in oil samples. PMID:26988510

When a chemical fuel at a certain position in a hybrid composite of the fuel and a micro/nanostructured material is ignited, chemical combustion occurs along the interface between the fuel and core materials. Simultaneously, dynamic changes in thermal and chemical potentials across the micro/nanostructured materials result in concomitant electrical energy generation induced by charge transfer in the form of a high-output voltage pulse. We demonstrate the entire procedure of a thermopower wave experiment, from synthesis to evaluation. Thermal chemical vapor deposition and the wet impregnation process are respectively employed for the synthesis of a multi-walledcarbon nanotube array and a hybrid composite of picric acid/sodium azide/multi-walledcarbon nanotubes. The prepared hybrid composites are used to fabricate a thermopower wave generator with connecting electrodes. The combustion of the hybrid composite is initiated by laser heating or Joule-heating, and the corresponding combustion propagation, direct electrical energy generation, and real-time temperature changes are measured using a high-speed microscopy system, an oscilloscope, and an optical pyrometer, respectively. Furthermore, the crucial strategies to be adopted in the synthesis of hybrid composite and initiation of their combustion that enhance the overall thermopower wave energy transfer are proposed. PMID:25938793

Preparing a stable suspension is a main step towards the electrophoretically depositing of homogeneous and dense composite coatings on NiTi for its biomedical application. In the present study, different composite suspensions of hydroxyapatite, silicon and multi-walledcarbon nano-tubes were prepared using n-butanol and triethanolamine as media and dispersing agent, respectively. Multi-walledcarbon nanotubes were first functionalized in the nitric acid vapor for 15 h at 175 °C, and then mixed into suspensions. Thermal desorption spectroscopy profiles indicate the formation of functional groups on multi-walledcarbon nano-tubes. An excellent suspension stability can be achieved for different amounts of triethanolamine. The amount of triethanolamine can be increased by adding a second component to a stable hydroxyapatite suspension due to an electrostatic interaction between components in suspension. The stability of composite suspension is less than that of the hydroxyapatite suspension, due to density differences, which under the gravitational force promote the demixing. The scanning electron microscopy images of the coatings surface show that more dense coatings are developed on NiTi substrate using electrophoretic deposition and sintering at 850 °C in the simultaneous presence of silicon and multi-walledcarbon nanotubes in the hydroxyapatite coatings. The atomic force microscopy results of the coatings surface represent that composite coatings of hydroxyapatite-20 wt.% silicon and hydroxyapatite-20 wt.% silicon-1 wt.% multi-walledcarbon nano-tubes with low zeta potential have rougher surfaces.

A facile approach was developed for the preparation of nanocomposite based on β-lactoglobulin (BLG)-functionalized multi-wallcarbon nanotubes (MWCNTs) and gold nanoparticles (GNPs) for the first time. Owing to the amphipathic nature, BLG can be adopted onto the surface of MWCNTs to form BLG-MWCNTs with uniform dispersion in water. Taking advantage of sulfhydryl groups on BLG-MWCNTs, GNPs were decorated on the BLG-MWCNTs-modified glassy carbon electrode (GCE) by electrodeposition. The nanocomposite was characterized by transmission electron microscopy, scanning electron microscopy and X-ray spectroscopy analysis. Cyclic voltammetry and chronoamperometric method were used to evaluate the electrocatalytic ability of the nanocomposite. Furthermore, a glucose biosensor was developed based on the immobilization of glucose oxidase with cross-linking in the matrix of bovine serum albumin (BSA) on the nanocomposite modified GCE. The resulting biosensor exhibited high sensitivity (3.98 μA mM(-1)), wider linear range (0.025-5.5 mM), low detection limit (1.1 μM at the signal-to-noise ratio of 3) and fast response time (within 7s) for glucose detection. PMID:24984286

In this paper, the electrochemical behaviors of rutin at the MWNTs-IL-Gel/glassy carbon electrode (GCE) were investigated. Good electrocatalysis behavior towards the oxidation of rutin with enhancement of the redox peak current and decrease of the peak-to-peak separation was demonstrated. The electrochemical parameters of rutin were calculated giving values of the charge-transfer coefficient (alpha) and the electrode reaction standard rate constant (k(s)) as 0.47 and 0.2s(-1), respectively. In addition, the MWNTs-IL-Gel/GCE was characterized by different methods including electrochemical impedance spectroscopy (EIS), scanning electron microscope (SEM), clay film thickness, and UV-vis spectra. The oxidation peak currents of rutin in such modified electrode increased linearly with the concentration of rutin in the range from 7.2 x 10(-8) to 6.0 x 10(-6) mol L(-1) with a detection limit of 2.0 x 10(-8) mol L(-1). These results suggest that the proposed electrode can be used for sensitive, simple and rapid determination of rutin. PMID:20708387

Accumulating evidence indicates that carbon nanotubes (CNTs) are biopersistent and can cause lung damage. With similar fibrous morphology and mode of exposure to asbestos, a known human carcinogen, growing concern has arisen for elevated risk of CNT-induced lung carcinogenesis; however, relatively little is known about the long-term carcinogenic effect of CNT. Neoplastic transformation is a key early event leading to carcinogenesis. We studied the ability of single- and multi-walled CNTs to induce neoplastic transformation of human lung epithelial cells compared to asbestos. Long-term (6-month) exposure of the cells to occupationally relevant concentrations of CNT in culture caused a neoplastic-like transformation phenotype as demonstrated by increased cell proliferation, anchorage-independent growth, invasion and angiogenesis. Whole-genome expression signature and protein expression analyses showed that single- and multi-walled CNTs shared similar signaling signatures which were distinct from asbestos. These results provide novel toxicogenomic information and suggest distinct particle-associated mechanisms of neoplasia promotion induced by CNTs and asbestos. PMID:23634900

Our data demonstrate that multi-walledcarbon nanotubes (MWCNTs) are internalized by macrophages, subsequently activating them to produce interleukin (IL)-12 (IL-12). This cytokine induced the proliferative response of T lymphocytes to a nonspecific mitogen and to ovalbumin (OVA). This increase in the proliferative response was accompanied by an increase in the expression of pro-inflammatory cytokines, such as interferon-gamma (IFNγ), tumor necrosis factor-alpha (TNFα) and IL-6, in mice inoculated with MWCNTs, whether or not they had been immunized with OVA. A decrease in the expression of transforming growth factor-beta (TGFβ) was observed in the mice treated with MWCNTs, whereas the suppression of the expression of both TGFβ and IL-10 was observed in mice that had been both treated and immunized. The activation of the T lymphocyte response by the pro-inflammatory cytokines leads to an increase in antibody production to OVA, suggesting the important immunostimulatory effect of carbon nanotubes.

In this article, direct coating of ZnO on PECVD-grown multi-walledcarbon nanotubes (MWCNTs) is achieved using atomic layer deposition (ALD). Transmission electron microscopy investigation shows that the deposited ZnO shell is continuous and uniform, in contrast to the previously reported particle morphology. The ZnO layer has a good crystalline quality as indicated by Raman and photoluminescence (PL) measurements. We also show that such ZnO layer can be used as seed layer for subsequent hydrothermal growth of ZnO nanorods, resulting in branched CNT-inorganic hybrid nanostructures. Potentially, this method can also apply to the fabrication of ZnO-based hybrid nanostructures on other carbon nanomaterials. PMID:21124621

In this article, direct coating of ZnO on PECVD-grown multi-walledcarbon nanotubes (MWCNTs) is achieved using atomic layer deposition (ALD). Transmission electron microscopy investigation shows that the deposited ZnO shell is continuous and uniform, in contrast to the previously reported particle morphology. The ZnO layer has a good crystalline quality as indicated by Raman and photoluminescence (PL) measurements. We also show that such ZnO layer can be used as seed layer for subsequent hydrothermal growth of ZnO nanorods, resulting in branched CNT-inorganic hybrid nanostructures. Potentially, this method can also apply to the fabrication of ZnO-based hybrid nanostructures on other carbon nanomaterials.

A well-reproducible and completely green route towards highly water dispersible multi-walledcarbon nanotubes (MWNT) is achieved by a non-invasive, polymer wrapping technique, where the polymer is adsorbed on the MWNT's surface. Simply mixing an amino-acid-based polymer derivative, namely poly methacryloyl β-alanine (PMBA) with purified MWNTs in distilled water resulted in the formation of PMBA-MWNT nanocomposite hybrids. Gold nanoparticles (AuNPs) were further anchored on the polymer-wrapped MWNTs, which were previously sonicated in distilled water, via the hydrogen bonding interaction between the carboxylic acid functional groups present in the polymer-modified MWNTs and the citrate-capped AuNPs. The surface morphologies and chemistries of the hybrids decorated with nanoparticles were characterized by transmission electron microscopy (TEM) and UV-visible absorption spectroscopy. Additionally, the composites were also prepared by the in situ free radical polymerization of the monomer, methacryloyl β-alanine (MBA), with MWNTs. Thus functionalized MWNTs were studied by thermogravimetric analysis (TGA), field emission scanning electron microscopy (FE-SEM) and TEM. Both methods were effective in the nanotube functionalization and ensured good dispersion and high stability in water over three months. Due to the presence of the high densities of carboxylic acid functionalities on the surface of CNTs, various colloidal nanocrystals can be attached to MWNTs.

Graphical abstract: After purification, the multi-wallcarbon nanotubes (MWCNTs) act as seeds for Fe{sub 3}O{sub 4} nanoparticles heterogeneous nucleation. The Fe{sub 3}O{sub 4} nanoparticles with diameter range of 4.2–10.0 nm synthesized in situ on the MWCNTs under solvothermal condition. The formed nano Fe{sub 3}O{sub 4}-MWCNTs decolorized the Acid Orange II effectively via Fenton-like reaction. Highlights: ► The amount of water tunes size and size distribution of the Fe{sub 3}O{sub 4} nanoparticles (FNs). ► FNs are homogeneously coated on the multi-walledcarbon nanotubes (MWCNTs). ► FNs have diameters in the range of 4.2–10.0 nm, average grain size of 7.4 nm. ► Fe{sub 3}O{sub 4}-MWCNTs are used as a Fenton-like catalyst to decompose Acid Orange II. ► Fe{sub 3}O{sub 4}-MWCNTs displayed a higher activity than nanometer-size Fe{sub 3}O{sub 4}. -- Abstract: Fe{sub 3}O{sub 4}-multi-walledcarbon nanotubes (Fe{sub 3}O{sub 4}-MWCNTs) hybrid materials were synthesized by a solvothermal process using acid treated MWCNTs and iron acetylacetonate in a mixed solution of ethylene glycol and ultrapure water. The materials were characterized using X-ray powder diffraction, scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, and vibrating sample magnetometry. The results showed that a small amount of water in the synthesis system played a role in controlling crystal phase formation, size of Fe{sub 3}O{sub 4}, and the homogeneous distribution of the Fe{sub 3}O{sub 4} nanoparticles deposited on the MWCNTs. The Fe{sub 3}O{sub 4} nanoparticles had diameters in the range of 4.2–10.0 nm. They displayed good superparamagnetism at room temperature and their magnetization was influenced by the reaction conditions. They were used as a Fenton-like catalyst to decompose Acid Orange II and displayed a higher activity than nanometer-size Fe{sub 3}O{sub 4}.

A modified carbon paste electrode (CPE) for the selective detection of dopamine (DA) in presence of large excess of ascorbic acid (AA) and uric acid (UA) at physiological pH has been fabricated by bulk modification of CPE with multi-walledcarbon nanotubes (MWCNTs) followed by electropolymerization of glycine (Gly). The surface morphology is compared using SEM images. The presence of nitrogen was confirmed by the energy dispersion X-ray spectroscopy (EDS) indicating the polymerization of Gly on the surface of the modified electrode. The impedance study indicates a better charge transfer kinetics for DA at CPE modified with MWCNT/polyglycine electrode. The presence of MWCNTs in carbon paste matrix triggers the extent of electropolymerization of Gly and imparts more selectivity towards DA by electrochemically not sensing AA below a concentration of 3.1×10(-4)M. Due to the exclusion of the signal for AA, the interference of AA in the determination of DA is totally ruled out by DPV method which is used for its detection at lower concentrations. Large peak separation, good sensitivity, reproducibility and stability allow this modified electrode to analyze DA individually and simultaneously along with AA and UA. Detection limit of DA was determined from differential pulse voltammetric (DPV) study and found to be 1.2×10(-8)M with a linear dynamic range of 5.0×10(-7)M to 4.0×10(-5)M. The practical analytical application of this electrode was demonstrated by measurement of DA content in dopamine hydrochloride injection and human blood serum. PMID:23770784

An electrochemical sensor for the amperometric determination of L-tryptophan (Trp) was fabricated by modifying the carbon paste electrode (CPE) with multi-walledcarbon nanotubes (MWCNTs) using drop cast method. 4.0 μL of the dispersion containing 2.0 mg of MWCNTs in 1.0 mL of ethanol was drop cast onto the electrode surface and dried in hot air oven to form a stable layer of MWCNTs. The electro-catalytic activity of the modified electrode towards the oxidation of Trp was thoroughly investigated. The modification with MWCNTs has greatly improved the current sensitivity of CPE for the oxidation of Trp. A very minimal amount of the modifier was required to achieve such a high sensitivity. The field emission scanning electron microscopy (FESEM) images revealed a uniform coverage of the surface of CPE by MWCNTs. Nyquist plots revealed the least charge transfer resistance for the modified electrode. The analytical performance of the modified electrode was examined using amperometry under hydro-dynamic conditions. The two linear dynamic ranges observed for Trp were 0.6-9.0 μM and 10.0-100.0 μM. The amperometric determination of Trp did not suffer any interference from other biomolecules. The detection limit of Trp at modified electrode was (3.30±0.37)×10(-8)M (S/N=3). The analytical applications of the modified electrode were demonstrated by estimating Trp in the spiked milk and biological fluid such as blood serum. The modified electrode showed good reproducibility, long-term stability and anti-fouling effects. PMID:23628203

In this work, covalently bonded graphene/carbon nanotube (Gr/CNT) conjoined materials are fabricated as engineered three-dimensional hybrid multilayer supercapacitors for high-performance integrated electrochemical energy storage. Stable aqueous dispersion of polymer-modified graphene sheets are prepared in the presence of cationic poly(ethyleneimine), PEI (PEI-Gr) for sequential or electrostatic layer-by-layer (E-LBL) self-assembly with negatively charged acid-oxidized or functionalized multi-walled CNT (fMWCNT), forming (PEI-Gr/fMWCNT)n architecture as "all carbon" super-capacitor, where n = 1, 2, 4, 6, 9, 12 and 15. These films possess an interconnected network of mesoporous nanocarbon structure with well-defined interfaces allowing sufficient surface adsorption and faster ion transport due to short diffusion distances. They exhibit nearly rectangular cyclic voltammograms at an exceedingly high scan rate of 1 V/s with an average specific capacitance of -450 F g(-1) and specific energy density of 75.5 Wh kg(-1) based on electrode weight, measured at a current density of 0.3 A g(-1), comparable to that of Ni metal hydride battery and charged/discharged within a few seconds or a minute. This is attributed to the maximized synergistic effect of the highest specific surface areas by preventing re-aggregation of PEI-Gr or PEI-rGO via fMWCNT as spacers. We also determined relative contributions of the interfacial capacitance (C(dl)) and charge transfer (R(ct)) properties of the hybrids and investigated interfacial properties by SECM technique. PMID:27483821

Polycarbonate fibers based single wall and multi-wall nanotubes (SWNT and MWNT) were prepared by first dispersing the nanotubes via solvent blending and/or melt extrusion followed by melt spinning the composites to facilitate nanotube alignment along the fiber axis. Morphological studies involving polarized Raman spectroscopy and wide angle X-ray scattering using a synchrotron radiation source show that reasonable levels of nanotube alignment are achievable. Detailed transmission electron microscopy (TEM) investigations on the polymer-extracted composite fibers reveal that MWNT more readily disperse within the PC matrix and have higher aspect ratios than do SWNT; extraction of the polymer from the composite prior to TEM imaging helps overcome the common issue of poor atomic contrast between the CNT and the organic matrix. Stress-strain analysis on the composites fibers show that MWNT, in general, provide greater stiffness and strength than those based on SWNT. Despite significant reinforcement of the polycarbonate, the level of reinforcement is far below what could be achieved if the nanotubes were completely dispersed and aligned along the fiber axis as predicted by composite theory.

Covalently functionalized multi-walledcarbon nanotubes (MWNTs) were prepared by grafting well-defined thermo-responsive poly(N-isopropylacrylamide) (PNIPAM) via click reactions. First, azide-terminated poly(N-isopropylacrylamide) (N3-PNIPAM) was synthesized by reversible addition fragmentation chain-transfer (RAFT) polymerization, and then the N₃-PNIPAM moiety was connected onto MWNTs by click chemistry. The products were characterized by means of FT-IR, TGA and TEM. The results show that the modification of MWNTs is very successful and MWNTs functionalized by N₃-PNIPAM (MWNTs-PNIPAM) have good solubility and stability in water. TEM images show the functionalized MWNTs are dispersed individually, indicating that the bundles of original MWNTs are separated into individual tubes by surface modification with polymer chains. These MWNTs modified with PNIPAM represent a potential nano-material for preparation of hydrophilic composite materials. PMID:23599017

We have prepared electrospun Nylon-6 nanofibers via electrospinning, and adsorbed multi-walledcarbon nanotubes (MWCNTs) onto the surface of Nylon-6 fibers using Triton® X-100 to form a MWCNTs/Nylon-6 nanofiber composite. The dispersed MWCNTs have been found to be stable in hexafluoroisopropanol for several months without precipitation. A MWCNTs/Nylon-6 nanofiber composite based chemical sensor has demonstrated its responsiveness towards a wide range of solvent vapours at room temperature and only mg quantities of MWCNTs were expended. The large surface area and porous nature of the electrospun Nylon-6/MWCNT nanofibers facilitates greater analyte permeability. The experimental analysis has indicated that the dipole moment, functional group and vapour pressure of the analytes determine the magnitude of the responsiveness. PMID:22389589

Environmentally friendly microstructure molds with montmorillonite (MMT) or multi-walledcarbon nanotube (MWCNT) reinforced polyethylene glycol diacrylate (PEGDA) nanocomposites have been prepared for miniaturized device applications. The micropatterning of MMT/PEGDA and MWCNT/PEGDA with 0.5 to 2.0 wt% of MMTs and MWCNTs was achieved through a UV curing process with micro-patterned masks. Hexagonal dot arrays and complex patterns for microstructures of the nanocomposites were produced and characterized with an optical microscope; their thermal properties were studied by thermogravimetric analysis (TGA). The TGA results showed that these nanocomposites were thermally stable up to 350 °C. Polydimethylsiloxane thin replicas with different microstructures were prepared by a casting method using the microstructured nanocomposites as molds. It is considered that these microstructure molds of the nanocomposites can be used as microchip molds to fabricate nanobio-chips and medical diagnostic chip devices. PMID:26726429

One-dimensional metal/semiconductor heterojunction nanomaterials have opened many new opportunities for future nanodevices because of their novel structures and unique electrical and optical properties. In this work, sulfhydryl-containing multi-walledcarbon nanotube/gold nanoparticle (MWCNT/Au) heterojunctions were synthesized in high yield by a sulfhydryl- functionalized self-assembly strategy. The component, size, structure, morphology and bond mode of the MWCNT/Au heterojunctions thus prepared were investigated and demonstrated by transmission electron microscopy, scanning electron microscopy, x-ray diffraction, energy-dispersive x-ray spectroscopy, Fourier-transform infrared and UV-visible measurements. Cyclic voltammogram and electrochemical impedance spectroscopy studies indicate that the MWCNT/Au heterojunctions have a novel electron transfer property, which retards electron transfer of the horseradish peroxidase or the ferricyanide in the underlying electrodes. We believe that MWCNT/Au heterojunctions with high stability and a unique electrical property are expected to find potential applications for nanodevices.

We studied the feasibility of using halloysite clay nanotubes (HNTs) and carboxyl-functionalised multi-walledcarbon nanotubes (COOH-MWCNTs) as antigen carriers to improve immune responses against a recombinant LipL32 protein (rLipL32). Immunisation using the HNTs or COOH-MWCNTs significantly increased the rLipL32-specific IgG antibody titres (p < 0.05) of Golden Syrian hamsters. None of the vaccines tested conferred protection against a challenge using a virulent Leptospira interrogans strain. These results demonstrated that nanotubes can be used as antigen carriers for delivery in hosts and the induction of a humoral immune response against purified leptospiral antigens used in subunit vaccine preparations. PMID:25742273

Multi-walledcarbon nanotubes (MWCNTs) coated with a smooth and uniform tin oxide (SnO 2) layers of different thickness were prepared by a novel thioglycolic acid assisted one-step wet chemical method. The coatings were characterized by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). The thickness of the SnO 2 coatings can be easily controlled by changing the synthesis conditions, such as pH value of the solution and hydrolysis time. The electrochemical properties of the SnO 2/MWCNTs composites as anode materials for lithium batteries were studied by galvanostatic method. The composites showed high charge capacities and good durability against decay. This could be ascribed to the good dispersion, thin layer and small particle size of SnO 2 on MWCNTs.

Multi-walledcarbon nanotubes have been synthesized at different temperatures ranging from 550 °C to 750 °C on silica supported Fe-Mo catalyst by chemical vapour deposition technique using Cymbopogen flexuous oil under nitrogen atmosphere. The as-grown MWNTs were characterized by scanning electron microscope (SEM), high resolution transmission electron microscope (HRTEM), X-ray diffraction analysis (XRD) and Raman spectral studies. The HRTEM and Raman spectroscopic studies confirmed the evolution of MWNTs with the outer diameter between 20 and 40 nm. The possibility of using as-grown MWNTs as an adsorbent for removal of As (V) ions from drinking water was studied. Adsorption isotherm data were interpreted by the Langmuir and Freundlich equations. Kinetic data were studied using Elovich, pseudo-first order and pseudo-second order equations in order to elucidate the reaction mechanism.

In this paper, we describe DNA electrochemical detection for genetically modified organism (GMO) based on multi-wallcarbon nanotubes (MWCNTs)-doped polypyrrole (PPy). DNA hybridization is studied by quartz crystal microbalance (QCM) and electrochemical impedance spectroscopy (EIS). An increase in DNA complementary target concentration results in a decrease in the faradic charge transfer resistance (R(ct)) and signifying "signal-on" behavior of MWCNTs-PPy-DNA system. QCM and EIS data indicated that the electroanalytical MWCNTs-PPy films were highly sensitive (as low as 4pM of target can be detected with QCM technique). In principle, this system can be suitable not only for DNA but also for protein biosensor construction. PMID:20006069

The multi-walledcarbon nanotubes (MWNTs) coated quartz wool (MWNTs/QW) prepared by dynamic layer-by-layer self-assembly was used as solid-phase extraction (SPE) absorbent for on-line separation and preconcentration of lysozyme in egg white. The coating procedures were performed continuously in a flow system operated by a set of sequential injection devices. The quartz wool was placed in a microcolumn forming a loose packing to guarantee the minimized flow impedance and the intimate contact between proteins and absorbent surface. Various parameters affecting SPE efficiency including the volume, pH, ionic strength and flow rate of sample and eluent were systematically studied. The feasibility of the proposed method was validated by successfully applied to the separation of lysozyme in egg white. PMID:22608421

One of challenges existing in fiber-based supercapacitors is how to achieve high energy density without compromising their rate stability. Owing to their unique physical, electronic, and electrochemical properties, two-dimensional (2D) nanomaterials, e.g., molybdenum disulfide (MoS2 ) and graphene, have attracted increasing research interest and been utilized as electrode materials in energy-related applications. Herein, by incorporating MoS2 and reduced graphene oxide (rGO) nanosheets into a well-aligned multi-walledcarbon nanotube (MWCNT) sheet followed by twisting, MoS2 -rGO/MWCNT and rGO/MWCNT fibers are fabricated, which can be used as the anode and cathode, respectively, for solid-state, flexible, asymmetric supercapacitors. This fiber-based asymmetric supercapacitor can operate in a wide potential window of 1.4 V with high Coulombic efficiency, good rate and cycling stability, and improved energy density. PMID:25694387

Multi-walledcarbon nanotubes (MWCNTs) were grown using iron oxide nanoclusters (Nc) assisted by self-assembled monolayer (SAM) on substrate. The amine-terminated SAM fabricated on silicon substrate (APTMS/SI) was carried out by UV-treatment and immersed into the FeCI3/HCI aqueous solution. Then, Nc were immobilized onto oxidized SAM silicon substrate (SAMs/Si) through electrostatic interaction between cationic Nc and anionic SAMs/Si. The characterization results clearly show that the well-graphitized MWCNTs were synthesized by using functionalized silicon substrate (Nc/SAMs/Si) as a template having appropriate density of catalyst. These consequences show that SAM containing template is important to achieve the effective layer of catalyst to synthesize MWCNTs in chemical vapor deposition (CVD). PMID:23901478

We report the preparation of Au nanoparticles synthetized by different protocols and supported on the surface of multi-walledcarbon nanotubes containing different functional groups, focusing on their electrochemical performance towards NADH oxidation, ethanol bioelectrocatalysis, and ethanol/O2 biofuel cell. We describe four different synthesis protocols: microwave-assisted heating, water-in-oil, and dendrimer-encapsulated nanoparticles using acid or thiol species in the extraction step. The physical characterization of the metallic nanoparticles indicated that both the synthetic protocol as well as the type of functional groups on the carbon nanotubes affect the final particle size (varying from 13.4 to 2.4 nm) and their distribution onto the carbon surface. Moreover, the electrochemical data indicated that these two factors also influence their performance toward the electrooxidation of NADH. We observed that the samples containing Au nanoparticles with smaller size leads to higher catalytic currents and also shifts the oxidation potential of the targeted reaction, which varied from 0.13 to -0.06 V vs Ag/AgCl. Ethanol/O2 biofuel cell tests indicated that the hybrid bioelectrodes containing smaller and better distributed Au nanoparticles on the surface of carbon nanotubes generates higher power output, confirming that the electrochemical regeneration of NAD+ plays an important role in the overall biofuel cell performance.

Paraffin-based solid fuels for hybrid rocket motor applications are recognized as a fastburning alternative to other fuel binders such as HTPB, but efforts to further improve the burning rate and mechanical properties of paraffin are still necessary. One approach that is considered in this study is to use multi-walledcarbon nanotubes (MWNT) as an additive to paraffin wax. Carbon nanotubes provide increased electrical and thermal conductivity to the solid-fuel grains to which they are added, which can improve the mass burning rate. Furthermore, the addition of ultra-fine aluminum particles to the paraffin/MWNT fuel grains can enhance regression rate of the solid fuel and the density impulse of the hybrid rocket. The multi-walledcarbon nanotubes also present the possibility of greatly improving the mechanical properties (e.g., tensile strength) of the paraffin-based solid-fuel grains. For casting these solid-fuel grains, various percentages of MWNT and aluminum particles will be added to the paraffin wax. Previous work has been published about the dispersion and mixing of carbon nanotubes.1 Another manufacturing method has been used for mixing the MWNT with a phenolic resin for ablative applications, and the manufacturing and mixing processes are well-documented in the literature.2 The cost of MWNT is a small fraction of single-walled nanotubes. This is a scale-up advantage as future applications and projects will require low cost additives to maintain cost effectiveness. Testing of the solid-fuel grains will be conducted in several steps. Dog bone samples will be cast and prepared for tensile testing. The fuel samples will also be analyzed using thermogravimetric analysis and a high-resolution scanning electron microscope (SEM). The SEM will allow for examination of the solid fuel grain for uniformity and consistency. The paraffin-based fuel grains will also be tested using two hybrid rocket test motors located at the Pennsylvania State University s High Pressure

We report magnetic measurements up to 1200 K on iron-contaminated multi-walledcarbon nanotube mats with a Quantum Design vibrating sample magnetometer. Extensive magnetic data consistently show a ferrromagnetic transition at about 1000 K and a ferromagnetic-like transition at about 1275 K. The ferromagnetic transition at about 1000 K is associated with an Fe impurity phase and its saturation magnetization is in quantitative agreement with the Fe concentration measured by an inductively coupled plasma mass spectrometer. On the other hand, the saturation magnetization for the ferromagnetic-like phase (at 1275 K) is about four orders of magnitude larger than that expected from the measured concentration of Co or CoFe. We show that this ultrahigh-temperature ferromagnetic-like behavior cannot be explained by ferromagnetism of any Fe-carbon phases, carbon-based phases, or magnetic impurities, but is consistent with the paramagnetic Meissner effect (orbital ferromagnetism) due to the existence of π Josephson junctions in a granular superconductor.

We report magnetic measurements up to 1200 K on iron-contaminated multi-walledcarbon nanotube mats with a Quantum Design vibrating sample magnetometer. Extensive magnetic data consistently show a ferrromagnetic transition at about 1000 K and a ferromagnetic-like transition at about 1275 K. The ferromagnetic transition at about 1000 K is associated with an Fe impurity phase and its saturation magnetization is in quantitative agreement with the Fe concentration measured by an inductively coupled plasma mass spectrometer. On the other hand, the saturation magnetization for the ferromagnetic-like phase (at 1275 K) is about four orders of magnitude larger than that expected from the measured concentration of Co or CoFe. We show that this ultrahigh-temperature ferromagnetic-like behavior cannot be explained by ferromagnetism of any Fe-carbon phases, carbon-based phases, or magnetic impurities, but is consistent with the paramagnetic Meissner effect (orbital ferromagnetism) due to the existence of π Josephson junctions in a granular superconductor.

A sensitive, selective and stable amperometric glucose biosensor employing novel PtPd bimetallic nanoparticles decorated on multi-walledcarbon nanotubes (PtPd-MWCNTs) was investigated. PtPd-MWCNTs were prepared by a modified Watanabe method, and characterized by XRD and TEM. The biosensor was constructed by immobilizing the PtPd-MWCNTs catalysts in a Nafion film on a glassy carbon electrode. An inner Naﬁon film coating was used to eliminate common interferents such as uric acid, ascorbic acid and fructose. Finally, a highly porous surface with an orderly three-dimensional network enzyme layer (CS-GA-GOx) was fabricated by electrodeposition. The resulting biosensor exhibited a good response to glucose with a wide linear range (0.062-14.07 mM) and a low detection limit 0.031 mM. The biosensor also showed a short response time (within 5 s), and a high sensitivity (112 μA mM(-1)cm(-2)). The Michaelis-Menten constant (K(m)) was determined as 3.3 mM. In addition, the biosensor exhibited high reproducibility, good storage stability and satisfactory anti-interference ability. The applicability of the biosensor to actual serum sample analysis was also evaluated. PMID:22277115

The effects of 170 keV proton irradiation for fluences of 5 × 1014 cm-2 and 5 × 1015 cm-2 on surface morphology and structure of multi-walledcarbon nanotubes (MWCNTs) film were investigated. The pristine and irradiated MWCNTs films were characterized using scanning electron microscopy (SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) spectroscopy. SEM analysis reveals that the proton irradiation for the high fluence of 5 × 1015 cm-2 leads to evident changes in morphology of the MWCNTs film, such as forming uneven film surface, entanglement of nanotubes and the shrinkage of nanotubes. Based on Raman spectroscopic and XPS analyses, it is confirmed that the proton exposure can improve the structural quality of the MWCNTs, and irradiation fluence plays a key role in reducing the disorder of the MWCNTs. This phenomenon could be mainly attributed to restructuring of the defect sites induced by knock-on atom displacements. EPR spectroscopy shows that electrons delocalized over carbon nanotubes increase with increasing irradiation fluence, implying that the MWCNTs film might be sensitive to ionizing radiation to some extent.

The effects of 3 MeV proton irradiation for fluences of 3.5 × 1010 cm-2 to 3.1 × 1012 cm-2 on structure and electrical conductivity of multi-walledcarbon nanotubes (MWCNTs) film were investigated. The pristine and the irradiated MWCNTs films were characterized using scanning electron microscopy (SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), elemental analysis (EA) and electron paramagnetic resonance (EPR) spectroscopy in order to investigate the effects of irradiation on their structure. Electrical conductivity of the MWCNTs films was characterized before and after irradiation. SEM analysis reveals that the proton irradiation for the high fluence (more than 3.6 × 1011 cm-2) leads to evident changes in morphology of the MWCNTs film, such as forming uneven film surface, curve, shrinkage and fragmentation of nanotubes. Based on Raman, XPS, FTIR and EA analyses, it is confirmed that the 3 MeV protons with high fluence (more than 3.6 × 1011 cm-2) can damage the structure of the MWCNTs, including increase of the disorder and the formation of functional groups. EPR spectroscopy shows that the electrons delocalized over carbon nanotubes increase with increasing irradiation fluence, implying that the MWCNTs film might be sensitive to ionizing radiation to some extent. With increasing the irradiation fluence, the electrical conductivity of the MWCNTs film decreases due to the structural and morphological damage.

A novel, simple and selective electrochemical method was developed for simultaneous determination of bisphenol F (BPF) and bisphenol AF (BPAF) in aqueous media (phosphate buffer solution, pH 6.0) on carboxyl functionalized multi-walledcarbon nanotubes modified glassy carbon electrode (MWCNT-COOH/GCE) using differential pulse voltammetry (DPV). In DPV, MWCNT-COOH/GCE could separate the oxidation peak potentials of BPF and BPAF present in the same solution though, at the bare GCE, the peak potentials were indistinguishable. The results showed that the electrochemical sensor exhibited excellent electrocatalytic activity towards the oxidation of the two analytes. The peak current in DPV of BPF and BPAF increased linearly with their concentration in the ranges of 0.6-1.6 mmol/L BPF and 0.6-1.6 mmol/L BPAF. The detection limits were 0.1243 mmol/L and 0.1742 mmol/L (S/N=3) correspondingly. The modified electrode was successfully used to simultaneously determine BPF and BPAF in real samples. PMID:25159400